You will pay extra, as in you will pay more than the ring is worth. If you buy a diamond ring, turn around and try to sell it back, they'll give you something like 30% for it.

This has always struck me as such a strange argument against buying a diamond ring, because it's true about every retail purchase. If you buy a chair, then turn around and try to sell it back to the store, you'd be lucky to get 30%, but no-one thinks that's an argument for sitting on the floor. You buy a chair because you want to sit on it, not as the start of a complicated chair-resale scheme. Similarly, you buy a diamond ring because you (or your beloved) want to wear it.

Note: I am not blaming you in particular, because this is a popular argument, but talk about a selective demand for rigour!