I believe it takes persistence, I have not found anything worth millions Lol, but I do find some good fabrics at the Salvation Army (Op) shop in the city when I visit, and over time I have gathered a small stash.
My best buys although not related in any way to quilting was years ago when I was a young girl I found some black earrings in a junk shop which the lady said were plastic, ( I thought differently) I cleaned them up to find they were sterling silver and onyx and I paid only 10c, they are now valued at about $150 dollars! The other thing was an old chiming clock which was made in 1913 in Germany, I paid $45 for it and at last count after I had it serviced a few years ago the clockmaker said it was worth $3,000!
These were things I bought a good many years ago tho!!
Gal