Like any Fiat Turbo they are either cherished or hammered. Council Estate Coupe 20VT's flooding the market for under £500 but have ruined the reputation of the mark enough for the concourse ones to be rendered virtually worthless if you were to take such an example to a dealer.
The Punto GT is a superb car in the right hands and a bloody nightmare in the wrong ones. Walk away from anything under £1000 and run if it's less than £500 or been modified.
The usual service history, old M.O.T's, original parts and listen to the seller. If it's a trader it's not as easy to spot but keep your ears pinned back for cleche's like...
"It goes like snot off a stick"
"It corners like it's on rails"
...and so on.
If the car is overpowered by air freshener or fabreeze, it's usually to cover the smell of burned rubber, fast food and joints, again walk away as the car is probably on the local Police watch list. New tyres are a good one as well. Why spend £££'s on new rubber if you only want £600 for the car? Have a look inside the front wheel arches for the remains of the old ones.
Another classic is full service history up to twenty or more thousand miles before the current owner. Basically they've come into a bit of money, bought a decent car and spent the last year or so ruining it. Depending how much of a hatchet job they've done it could be salvageable but pay salvage money.
The Punto GT is starting the get the same cult following as the Uno Turbo and justifiably so. It may weigh a little more and is a little bit slower but thanks to the Joy rider generation these cars will be collectors items soon so if you have the time or budget to get hold of a decent one; think of the car as an investment rather than a "like well buff 'ot 'atch innit bruv" and you should see a couple of years or free motoring as the car won't depreciate any more and could even go up in value.
Choose wisely and you can't go wrong.