depends on the product.
Buying a pipe sight unseen?
If it's eBay, I'm less concerned because of its money back guarantee. It's even less of a factor if the item is from overseas as I know I would not pay to return anyway. In general, I find eBay favors the buyer, so I don't let no returns deter me.
I agree with smudgersmissinglegUnless it's something really cheap i'd avoid sellers with a no returns policy.