Sounds like a good idea, seems too big for Flippa if you ask me. Have you asked any of the sites mentioned above if they're interested? Or a largely offline company?
The problem came because on the visa form it said occupation and singer was put down. When asked why she was there, she said holiday. Then being too honest when asked, she said she had some small non-paying gigs. I can understand how this might lead to secondary inspection but after phoning the venue (who told her they were non-paying, small and promotional) the immigration official went off on a lie claiming she knows how many thousands of pounds my friend was going to be paid and that they were big events (small open mic at a pub where my friend could do a few songs for London friends). The woman even admitted to me hours later that she made a mistake but claimed she couldn't reverse the paperwork.
There is no ESTA to fill in going to the UK from the US (that I'm aware of anyway). No rules were being broken either. Just being too honest and excited coupled with not fully realising she should've just said on holiday and nothing else. I get to deal with changing rules and paperwork and being at the mercy of the mood of an immigration official all the time too, so I don't think it's just you or a certain kind of person.
I've realised a good analogy would be if a golfer was going somewhere on holidays and was going to play a few rounds of leisurely golf with friends while he was there.
The thing with the woman officer who stopped my friend and then interviewed her was that woman lied saying that she phoned music venues and they told her how many thousands of pounds my friend was going to be making. Completely. Ridiculously. Fabricated. Just started making stuff up to back up her case.
During the second interview in the back room it was fully explained why my friend was there. The woman in charge then told her "It doesn't really matter what you tell me now anyway, I'm going to base it off what you said the first time around." Even after I got to explain the thing again on the phone to the woman later she said if that's the case she made a mistake but there was nothing she could do about it at that point as she "just stamped the paperwork so no reversing it now."
Hard to say really, didn't work in this case. Another friend of mine has been told before by passport control to just say "tourist" when she gave an answer that wasn't "I'm here on holiday" whereas customs then grilled her minutes later on why she said "tourist" when she was there for a wedding.
Same boat as you. Never had any close calls before though, went to Ireland recently via Heathrow and had no problem, gave the exact same info. All seems to be down to the officer in charge and the mood they are in. Show up early and dress well for a chance to get bumped up.
This was suggested by one of the people I spoke to afterwards. They can now say that they don't just stop a certain kind of group or look... "We stopped a blonde American girl last week."