Wrong forum for a start - try Motors.
But in answer to your question:-
1. Avoid Selespeed like the plague. Horrific reliability problems with those boxes which can cost £thousands (yes, thousands) to fix. How does the car dropping you into neutral as your pulling into a high speed roundabout grab you?
2. 147s are noticeably more expensive to maintain than other cars in their class. Components don't last long so often need replacing.
3. Full service history ALWAYS.
4. Make sure you have evidence of the cambelt, balancer belt and variator being changed every 36k. If it hasn't been regularly changed, BANG, there goes your engine.
5. A well looked after car will be okay. Look for a car with a lot of receipt, and signs that money has been spent on it.
6. They use oil. Can be as much as 1ltr / 1000 miles, so ask the owner a general question about how often he tops up. If he doesn't have a clue, walk away. Its not one of those cars that never needs a top up between services. If its ever been run low on oil, that's the end of your engine.