It really depends on your area but yeah in general the entire secondhand market has gone to absolute shit because "the secret is out." There's a million people trying to make a quick buck by buying anything of value and flipping it over Facebook marketplace or so on.
I think it's a sign of the economy getting shittier personally, as well as people being disenchanted with their jobs: everyone and their mother has a "side hustle" and is trying to pull some sort of money making scheme nowadays, it seems. The internet has also made it worse ofc. It's extremely rare to find things that are underpriced nowadays because the thrift store owners/whoever can just google it and find out exactly what it's going for on ebay.
You have to be in the right place at the right time, but unfortunately the scalpers are putting in even more effort to find all those places.
One of my friends picked up an upholstered cat tree secondhand and just immediately brought it into his house and let his cats sleep on it. I said holy shit lol did you check it for bugs???? He had not even thought about it. It didn't have bedbugs luckily...... but it did have rat shit on it. I'm pretty big into thrifting and furnished half my old apartment that way, but come on guys, there's two simple rules:
1) Properly clean/sanitize anything before you wear it/keep it in your house.
2) Don't buy anything that you DON'T have the ability or equipment to clean/sanitize, especially upholstered furniture.
My local Goodwill used to sell clothes for pennies on the dollars, especially as a kid I remember most of my winter clothes came from there. Now I swear sometimes they're selling the clothes for more than they originally would have cost a few years back, and you never see anything quality. It's all Walmart-level plastic puff jackets with stains in them for 25 dollars, when Walmart was probably selling it for 19.99 back in 2020.
My favorite thrift store is one in a weird area of town run by a church that's all hoarded up and just about gives you an asthma attack by stepping inside. It's also about 95% total garbage in every sense of the word, but the difference is that the nice church ladies that run it are 100% aware that it's garbage and almost everything is under 5 dollars. So if you do manage to find something that's nice, you're probably going to get a good deal. I think I told this story before, but I found a tin full of artist quality oil paints- probably about 80-150 dollars worth, as I couldn't tell how much was in the tubes- and there was no price on it. The actual pastor of the church was working the register and just shrugged and said, "7 bucks?" so that was a pretty good deal and I still use those paints. I bought mason jars for a quarter each: the other thrift store was selling them for 5 dollars a pop, seriously. Children's books are a dime each- most adult books are 50 cents- cookbooks and hardbacks are a dollar, and all their religious stuff is free. You'd think that'd be the norm but the other thrift store in town- which is also run by a Christian organization- has the bibles for free but all their devotionals and inspirational etc are still basically just half-price books, we're talking 5-7 dollars for a single stupid paperback.