iamnicolas, hi.
Are you intending on buying a second hand 500 or considering purchasing new?
If buying second hand, then make sure you do your research properly and inspect well. There are a lot of 500's most in good shape and are a good buy, but there are a lot of cars which have either had little or minimal servicing regimes. Don't forget, the economy has gone through a downturn, this means that there are plenty of car owners who will do the absolute minimum in terms of either servicing, or in lots of cases, none at all. A genuine service history is therefore a really good indicator the car has been looked after. Don't forget too, you've got more rights buying from a franchise/independent dealer, than you have buying privately. If buying from a dealership, pay the deposit on a credit card as you have rights under the Consumer Credit Act should anything go wrong.
If you've read through the forum, by now, you'll have gathered the most common issues that 500 owners suffer, door handle hinges, tail gate wiring etc. Also, with the 1.2, the cambelt and waterpump will require changing either at the four year point or I believe 72k miles? If this hasn't been done and you're buying a car over 4 years or older, make sure it is or ensure the cost of replacement is deducted from the sale price.
If you are not comfortable doing a full thorough inspection prior to purchase yourself, it may be worth paying someone who does know what they're doing, such as one of the motoring organisations that offer that type of service. After all, if you're spending a few £k on a vehicle you might have for a few years, surely you want to be as sure as you can be, that you've not bought a lemon. I would say, buying from a Fiat dealership for instance, would ensure that the car has had a thorough check, any safety/recall work done and all appropriate software updates applied. Granted, those cars will cost you more, but you do have an element of safeguard and guarantee.
Read this thread for an idea of just how horribly things can go wrong!:
https://www.fiatforum.com/500/353692-engine-mount-snapped-my-fiat-500-2011-lounge.html