Sold my last one on Gumtree, Was offered £2k trade in, (similar in garages were around £3k) I put it up for £2.9k and accepted £2.5k in the end.
You have to hold a firm line with nobs, anyone offering cash without looking / test driving it is 99% wasting your time. If you price it sensibly you will get genuine buyers and you just need to put a bit of time in and be reasonable in accepting an offer. Good luck.