I also sort out the car boot sales – I've never managed to find the really good stuff, (I live in Coventry, so a lot of the time, the stuff being sold looks like it has been used to plough a field), but have found assorted games and some consoles that have worked.
One of my proudest moments was buying two non-working Game Gears, for 50p and 20p and then fiddling about until I got one of them working. Sadly, I had to sell it a few years back to help pay vet bills for one of our cats who had presumably tried wrestling a car.
I did miss out on what looked like a vintage Atari 2600 by about 30 seconds a few months back (which was a real shame, as I've never owned one). I was gutted for days!
The best non-gaming bargain I've found was a Force FX lightsaber, for sale for £10.00*. It was being sold by one of those stalls where it looks like they sell stock from bankrupt companies. Evidently, they had no idea what they were selling, as I asked to take a look at it, pulled an uncertain face and asked how much. When the sum of £10.00 was mentioned, I 'grudgingly' agreed, paid up and legged it to the exit, giggling all the way!
Even better, when I got home, I tested it and it worked perfectly!
*For those who don't know, these were being sold for anywhere between £80.00 and £120.00 at the time – dependent on where you shopped.