Honestly, I feel you. There's a lot of garbage (for a sampling head that is) that is dumped at thrift stores that is mostly completely useless for sample based music / 90s era or lofi hiphop beats. It's almost impossible to determine this just by looking at a cover, reading a band name or looking at some of the text on the cover. You're also very likely going to be the 20th person to dig through the piles of records nobody wants.

Some of my best finds were hidden very deep, part of buying a huge record collection online secondhand (something like eBay / craigslist, but a local one). Still has loads of trash I can do very little with, except for the tiniest of samples. Forget about loops though. You'll need some of the better soul or jazz records for that. And some of the older stuff, is truly old (50s 60s era). It's unlikely going to fit in modern music production.

At the same time I have to admit I'm not even that great at finding loops even on great records and I do think some people can turn almost anything into sampled gold. But the whole thrift store thing selling records at $5 a piece with 99 out of 100 being trash is definitely frustrating. Definitely has made me invest more in sample packs and record actual instruments or sounds myself. I had more use from walking around town with a ZOOM H2N, than any of my latest hours of digging in what really were simply terrible records to sample from.

Yes, occasionally you will find useful drum breaks or like a snare, separate hi-hat or kick or even the worst records, but imagine finding only a barely usable snare on a single record. It's funny people mention Christmas records. I also came across a lot of 'top40' style collections. I have like 6 records featuring Michael Jackson's Beat It, 4 records with Staying Alive, etc... No more 'song collections' for me if I can avoid it. But I will continue to buy some secondhand collections online I think regardless.