I agree that a lot of traders do MOT the car after sale, however this is annoying if you are travelling a long distance. As even if you took the readies and had the means to get it back on the day of viewing, you would still have to make another trip to go and pick it up. If it is the right car then its worth it, if not its a wasted day and money.
I have lost count of the days I have wasted driving up and down the UK to look at what are advertised and pictured as good cars but turn into dogs once you get there. Some of these I have looked at have been XMs. As a result I'm quite put off by buying cars now, unless they are from forumers, which is where three of my cars have came from
It's all down to the seller really.