Hi, as you've mentioned 4 websites on your original posting that are failing you, assuming your sales expectations are realistic in today's financial pressured times, then I'd perhaps question whether my adverts really are written as well as I think, are the photos really that good & are my prices really reasonable?
What's your stock profile??
I've never took the plunge with AT as being a small operation at the lower end of the market I couldn't justify the fees & as for a website, well, unless someone knew my website address they're not going to find me on the 5th (or 25th) page of Google - they'll simply find you via the main platform.
I think a lot of your advertising focus may depend on your stock profile & aiming it at the correct audience. I'm sure for "specialised" or newer cars then AT is the way to go. A couple of the main dealers I've bought trade-ins from recently have said Motors is doing ok for them, oddly enough they say it's an older crowd buying from there.
Personally I think Gumtree's ok for selling a filthy £30 cooker or a set of scuffed alloys with half-bald tyres but that's about the financial limit on that website. I'm sure others will disagree but I reckon it's a waste of time - I wouldn't even spend time uploading a car even if it was free to use. The same with Facebook as most on there seem to be the part-time brigade or those masquerading as "private" but in reality "full-time selling pure shite" but again, I'm sure others will disagree.