I like to pick the garage sales, estate sales, GW & SA, collector's shops, and antique shops on occasion, but these folks are not record people. Everyone now thinks every piece of vinyl, especially very common Beatles records and even Jim Nabors, etc., must be priceless. Some record shops have followed that lead, trying to "cash in while the medium is hot."
I have found about three shops where I know the people, can trust them, and see that their records are in great condition, and graded properly in general-- often sight-graded but sometimes play-graded too (it depends how busy these guys are and how many records they are dealing with). Two of them I would consider "friends," and I'm a pretty loyal guy and I also like to spend locally when I can, rather than order on-line unless there is a significant savings; i.e., I have paid a few bucks more to give the business to my favorite shops, even when ordering new product.
But I have been frequenting one amazing shop that I call the "honey hole;" this guy has been both a collector and dealer (weekends at an antique flea market) for years, and is starting to divest himself of his personal collection which must be in the tens of thousands. Not quite yet, but he's thinking about retirement and selling his house and getting rid of a significant chunk. So he took over a local shop and is now open weekdays as well. His stuff is immaculate, and he has lots and lots of great records in the genres I like.
I would much rather spend my money with guys like this ^^^^, than with the fly-by-night cash-in types I have had some experiences with. I bought a decent record from a kiosk guy in an antique shop. The next time I went back and picked-up something else (even though it was "used," but he had it "sealed" in a sleeve with gobs of tape), I was disappointed after paying a premium price and then taking it home to find more or less a $3 record inside (beat to ****). The next time I was in that store, there was a nice-looking piece that I was interested in, "sealed" up the same way, with a note saying "do not open." I ignored that, opened the outer sleeve to find another craptastic piece at inflated prices, and I have never purchased from that seller again.
Take your time and find the right vendors. Then buy from them.
GJ