Yes, he's an odd one. I've had a good deal with him, no problems at all, and Mark says he's OK f-to-f. But he turned on a friend of mine for some imagined slight and never spoke to him again. I've heard numerous negative things about him since. Clearly has personality 'issues'...
So, as you say, collectors beware, especially when dealing with a 'Keith' or 'Peter' from Newmarket.