Look up on autotrader how much similar cars are advertised for. Personally I think you'd be very lucky to get £3k. To get more, you're going to need it to be pristine and have less than 40k on the clock.
Autotrader is expensive to advertise on and their prices have just gone up, also they are stopping the print magazine, so all new adverts will be online only. If your car is worth less than £1k, the it's £9.99 for web only advert. But over £1k and you're talking £24+.
Piston heads now charges. But I did sell my old Alfa 156 with knackered gearbox through that, before they started charging.
I've not had any joy with selling cars on Gumtree, probably partly due to the way they order the adverts. But the adverts are free, unless you want to feature it or repost it to bump it up to the top.
Don't even bother with Webuyanycar or similar, they'll give you about 20p. Just read the reviews. They "offer" you £3,000 on the online valuation, then take it for inspection and they'll knock 50% off instantly.
A part exchange with the dealer would probably get you more than WBAC.
Good luck.
