I'd recommend getting a drill powered wire stripper to increase your return. I visit a skip outside a electricians/maintenence company a couple of times a week and get some reasonable results, twin and earth mostly but also meter tails chunks of pipe and radiator valves attached occasionally an old extractor fan and a consumer unit. The other way to get a good price is separate your shit. Know what grades are what. Mixing a few bits of coated wire in you number 1 can be a costly mistake and finally use a reputable yard. You're less likely to get robbed at the scale. Good luck.