"How do you know the items you sell/buy are authentic?"

When in doubt, always seek professional opinion. Stores like Holts or individual boutiques will often ban their employees from authenticating items due to liability issues. Thus, there are professional authenticators out there. Even so, it's always good to arm yourself with some knowledge when it comes to these designer items. Below is a helpful authentication guide for Chanel (taken from Yoogi's Closet: http://www.yoogiscloset.com/authenticate/chanel)

Chanel Authentication Guide & Serial Codes

Serial Number Year Manufactured Style of Numbers Style of Serial Number Sticker Picture of Serial Number Sticker 18XXXXXX 2013 to 2014 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 17XXXXXX 2012 to 2013 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 16XXXXXX 2012 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 15XXXXXX 2011 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 14XXXXXX 2010 to 2011 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 13XXXXXX 2009 to 2010 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 12XXXXXX 2008 to 2009 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 11XXXXXX 2006 to 2008 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 10XXXXXX 2005 to 2006 0's have strikethroughs. 1's have small serifs (feet). Eight digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 9XXXXXX 2004 to 2005 0's have strikethroughs. 1's have small serifs (feet). Seven digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 8XXXXXX 2003 to 2004 0's have strikethroughs. 1's have small serifs (feet). Seven digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 7XXXXXX 2002 to 2003 0's have strikethroughs. 1's have small serifs (feet). Seven digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 6XXXXXX 2000 to 2002 0's have strikethroughs. 1's have small serifs (feet). Seven digit serial number printed on white sticker covered with clear tape with two Chanel logos."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 5XXXXXX 1997 to 1999 0's have strikethroughs up to 51XXXXX. 0's have no strikethroughs from 52XXXXX to 56XXXXX. 0's have strikethroughs from 57XXXXX on. 1's have small serifs (feet) from 57XXXXX on. Seven digit serial number printed on white sticker covered with clear tape with two Chanel logos from 57XXXXX on."X" cut-lines prevent sticker from being removed without damage. "CHANEL" appears on rightright side of the sticker. Dark line appears on left side of sticker. Gold speckles appear throughout sticker. 4XXXXXX 1996 to 1997 0's have strikethroughs. 1's are sans-serifs (no feet). Seven digit serial number printed on white sticker with Chanel logos. Opaque film covers sticker. 3XXXXXX 1994 to 1996 0's have strikethroughs. 1's are sans-serifs (no feet). Seven digit serial number printed on white sticker with Chanel logos. Opaque film covers sticker. 2XXXXXX 1991 to 1994 0's have no strikethroughs up to 27XXXXXX. 1's have serifs (feet). Seven digit serial number printed on white sticker with Chanel logos. Opaque film covers sticker. 1XXXXXX 1989 to 1991 0's have no strikethroughs. 1's have serifs (feet). Seven digit serial number printed on white sticker with Chanel logos and left-sided cutout. Opaque film covers sticker. 0XXXXXX 1986 to 1988 0's have no strikethroughs. 1's have serifs (feet). Seven digit serial number printed on white sticker with Chanel logos and left-sided cutout. Opaque film covers sticker. Note that early serial numbers (starting with a 1 or 2) did not have a leading "0". Therefore, these were six-digit serial numbers. Also, the sticker was larger than the stickers produced later in the series.