To buy or not to buy

I am confused.

I saw a good deal of SK II product on ebay. The problem lies with the price, it is too cheap for a genuine SK II product.I contacted the seller and she assured me that it's an authentic product and she got a good rating from her previous buyer. Sounds too good to be true.

Now should I or should I not buy the product?

Also, any review on Olay product for dry skin?

Whoever read this, please help.