Some of the Gbase dealers, like "Gary's", don't have retail stores, he keeps his guitars at his house. He has expenses for advertising and guitar shows, but I'll wager a guess he can afford to sit on all of his guitars if he needed to.
Mike's Music pays the rent on a small volume of higher dollar pieces. His two stores are in moderate to low rent neighborhoods and he doesn't pay his employees much. Most of the stock on regular display in the stores has been there for a while, and the bulk of it is priced over market value. A good percentage of it is currently broken and/or has non original parts or mods and even with those issues, is still over market value for clean pieces. Some of his prices almost seem like practical jokes. He's had this one thing for at least 5 years, it's a box with a small tube amp and speaker that I'm fairly certain was originally packaged with an Italian electronic organ that was imported to England. The original logo is gone, there's just a bare rectangle down to the wood where it was literally cut off the grille cloth, but it has the same kind of blue/grey covering as 60s Selmer amps from England did (which was also used by several other makers). The amp chassis is definitely English, is low wattage, has no visible controls - just an output jack (the controls presumably were on the organ, which was also hard wired to the amp input), and it has a small ish speaker, probably a Goodmans. There is no indication of maker whatsover, the exterior is in only fair condition, and the amp needs an overhaul. As someone quite familiar with oddball 60s British amps, I would estimate this piece, of awkward size, unknown make, and unknown but almost certainly non guitar application, to be worth maybe $250 as a generous estimate. I have bought cooler vintage oddball amps on ebay from England for under $100 before shipping, but whatever. This piece at Mike's, however, is tagged as a Selmer and priced at $1500 ! That's more than all but the few most desirable Selmer guitar amps would typically fetch in clean examples, more than I paid for any of the 6 I own including a pretty clean Zodiac 30 with original cone alnico Celestions.
These guys know that stuff listed on Gbase will probably be seen by a lot of folks and stay on there for a while, so they overprice there in hopes of upping the perceived going rate for those doing quick web searches for stuff that is not that common. Whatever the going rate is, is just a kind of group faith that that's what others are paying or have paid, along with the perception of how cool and how desirable something is, supply and demand are both dealt with through human estimation in this market and as such they can be manipulated. It's not like the stock market or real estate where everybody can basically see what something sells for.
They sell some pieces at the speculatively high prices - some people don't care about the price, or aren't patient enough to shop around, and other pieces sell for less, or bring in traffic and interest that benefits them later.