I know this is all pie in the sky talk, but I can give a pretty useful contribution on this exact topic.
As some of you have seen, for the last year I have been 'dealing' in retro consoles and games. I stopped recently because it was just taking up too much time (my whole life basically!) but it certainly IS possible to turn over a decent profit on a large-ish scale by buying and reselling old computers/games/toys/whatever. But there are a few conditions:
1) It is a LOT of work. Hours every day scouring eBay, forums etc, not to mention photographing/listing/posting everything. Doing it properly is near a full time job. You have to be organised and pretty ruthless/disciplined.
2) If you put the work in as above, it is possible to make a decent profit on most things you sell. I averaged about £70 per console, and £25 per game. But to get top prices often takes time, so sometimes you will have items 'in stock' for weeks/months.
3) As with buying, occasionally you will get burned. Lost in the post, damaged, over estimated resale value etc. You won't win them all.
4) You are completely at the mercy at what comes up for sale, sometimes I'd go weeks without finding anything, and then other times 5 things would come up in one day. So you need both capital to buy, and not to rely on the money.
Taking the above in to account, adding x amount per week on top of the above for overheads of a premises, plus the dry spells, personally I wouldn't rely on it for an income or set up a physical store unless subsidised by something else (coffee is a good idea.) But as a sideline to your job, it can be great.
I'm sure any of you that deal in SW can relate to a lot of the above.