I think it can be risky, unless you really know what you are looking at. I have never heard of buy now, pay later either.
My mom bought my grandmother a new e-ring in the islands when she was there on business on my grandfather's behalf. However, he wanted to spend no more than 1k on the whole thing but wanted at least .75 stone! She ended up getting her a .75 or somewhere around there solitaire in yellow gold that is likely about L-N in color- it does have a very, very visible tint for about $800. I have no idea about the quality of the stone or the cut. It does sparkle, but really, what do you get for $800 in that weight? Not much, I expect. He's just cheap and spends money on himself, but not her...