I've had similar experiences. The way I look at it is they didn't want to put the effort into learning what they were selling to maximize their profit. I'm not robbing them, just taking advantage of their laziness.Just got an unexpected deal at a local gun store... They had a bin of unpriced "Misc" pistol mags. Found two standard 8rd Tokarev mags and a 9rd Yugo M57 mag. None of them had any markings, so they may all be newer commercial production, but they look decent, so im happy. These mags go for $25 - 40 each online, but the guy gave me all 3 for $20 (total) after telling me he was pretty sure they were 1911 mags. I kind of feel like I robbed them, but they obviously didnt know what they had.
Now, if it's a good friend, I will say something about their pricing, but a good friend will likely not care as they know that I will return the favor.