I buy loads and loads of old vinyl records from various discount bins, flea markets and thrift stores. If it's 1 or 2 €: I often just buy blind if cover is somewhat appealing to me or because artists names ring a bell for me.
If I like what I hear, I obtain an mp3 copy of it (various sources) for my library. If I really liked it and can't find it digitally (it happens): I record my own vinyl record to have a digital copy. My file preference is mp3 VBR. I think flac is overkill for most basic soundsystems and human ears and they are not worth the enormous filesize difference.