The thing is, you cant always tell who is wasting your time. I had an email enquiry last week which was a part ex lead through AT, Details of car, I looked it up on dvla MOT history, it had failed its MOT a week before on corrosion.
I called the customer, she said, 'I might come down saturday, but I havent seen one of these (my car) before, and I'm on holiday in a week so not in a rush to buy, probably make my mind up when I'm back in 2 weeks'.
She rings on saturday morning to say 'I'm on the way'. I'm not full of hope on this but still do it right - check theres a bit of fuel in it, clean it off, all paperwork ready to inspect.
She turns up, and asks about the price on her p/ex, which she hasnt brought with her (for obvious reasons, but she still hasnt told me that). I just say I wouldnt want it because of the MOT fail. So we take my car out for a drive, little haggle on return, deposit taken and car has gone this morning.
So from someone who knew nothing about my car, and was telling me she wouldnt be buying on the day(or even in the next fortnight) to fully paid and gone within 48 hours. It would've been really easy to dismiss this out of hand. Unless youre really busy or taken the AD route, give them all a chance. they will let you down. But sometimes they will (pleasantly) surprise you. Sometimes the lies they tell you are good ones!