Greatest Stamp Scores/Purchases?

That's really interesting Bob. I found a collection of Jamaica a number of years ago on Apfelbaum's site, and it had in full view a quite-rare variety of the KGVI 10/- definitive, mint (line perf 14, which is listed in Gibbons for something like GBP 6,500). I think the entire collection cost me a few hundred, so this was a major score and perhaps additional proof that Apfelbaum's is nothing more than a purveyor of "shovel wear."

That was the second time I found a mint copy of Jamaica line perf. I had found one in a red box at a local show in Florida around 2008 or so for the princely sum of $7.

Don't knock eABY. Found a 1805 stampless letter from Philadelphia addressed to Lawrenceburgh, Indiana four months before the PO opened. It was sent via Cincinnati, Ohio to a man "who may have relocated to Lawrenceburgh". It was delivered to him there.

In the late 80s, I traded 2 bent mag wheels (they were left at my house by a cousin so no cost to me) to a guy for a couple of older stamp references and a large box (roughly 4 ft long) of modern used covers with modern official stamps on them. The box came from internal communications to the main Tennessee National Guard office from other Tennessee offices, as they were one of the US departments that required the use of the official stamps. This box included eight covers with the $5 official stamp and about a dozen with $1 stamps, and all of the lower denominations in various combinations. I sold and traded most of them over the next few months for about $300 retail value. Not the biggest score on this list but it was fun for a relatively young collector.

I bought a cover on ebay from I believe 1911, that had about 8 different stamps, and a line pair of Scott 386, with a hand-written note for the cover to be saved for the son of the recipient. Most likely other viewers/bidders didn't notice the line pair (photo wasn't great), but appeared to be the line pair to me, and I figured I'd gamble. It could be considered a philatelic cover, but the used line pair now catalogs $2500 off-cover. I got the cover for $58 and sold it at auction for $850. Still find good buys on ebay frequently enough to go fishing there.