My Mum really enjoys doing jigsaw puzzles but for decent ones they're normally about £10.99 each, which she thinks is stupid for something she'll probably only do once (and then get rid of because they take up a lot of space). So whenever I see a good one in a charity shop I get it for her. Sometimes I do it first to check all the pieces are there, other times I just hope they are (they always have been so far!).
It means she can have more presents as they're normally about £1.99 from charity shops, and she doesn't have to feel bad passing it onto somebody else or back to a charity shop once she's done it.
As long as things are in a good condition I don't really see a problem with it, especially when people are struggling to buy day-to-day things. I reckon once I've got a LO to buy things for I'll be buying even more things second hand, especially things that they'll only be interested in for a little while.