There are a few things to remember when buying Lancome on eBay.  I don't wear Lancome makeup (save for l'extreme mascara) but I've worked from Lancome for years and know the products well.  When next you buy remember the following:

Lancome skin care products are made almost exclusively in the USA, occasionally in France and as far as I know - nowhere else - especially not in China.  Be very wary of items coming from China.  If it's too good to be true, it probably is.

ALL Lancome skin care products have a unique serial number embossed on their package.  Any seller of authentic Lancome items should be able to provide you with this number.

Lancome products don't smell like "bug spray" or "vics vapo-rub".  All Lancome products have a pleasant, subtle floral smell.  If a seller tells you the formula is different because it's been imported or anything of the sort, request an immediate refund and don't put the product on your skin.

Good luck and happy bidding!