I pressume you've seen the car before you commited to buy it? If not, you really don't know what you have bought.
I hope it turns out to be a really good car. If it is then it is a bargain at £800. If it isn't, then you've only got yourself to blame for agreeing to buy it without seeing it first.
If you have concerns about getting it home, then I would advise that you trailer it. If you don't have a suitable towing vehicle, you must know someone who does and trailers can be hired for not too much money.
When buying a car from 500 miles away with just a few small photos to go off, you have to factor in a contingency fund to go towards transporting it back home and repairing it should anything need doing.
Good luck, and I hope it turns out to be a good one. If it isn't then put yourself in the sellers shoes and think how you would react if your buyer pulled out.
