There is someone who makes a living out of driving to Ikea everyday and collecting flat pack furniture for people. I believe he'll also assemble it if you wish.
I'm pretty inept around the house, handyman wise, but I've never had a flat-pack that I couldn't put together. I agree that the quality is usually so low with these things that a) I'd try not to but it any more and b) It's not worth paying someone else to do it.
Someone out there probably can't but that 1% of people will likely have friends / family and if not then unlikely to have the money to buy the packs let alone put them together. The few people who would somehow fit your 'market' seem to have loads of people offering to do it at a price, it's the advertising yourself that they seem to miss (and should cost more than the profit fom doing the work anyway).