Personally, I would rather save the dosh, support a local independent (so long as they have a good reputation) and spend the savings on more mods  If you're worried about any warranty implications, so long as the garage is UK VAT registered, Fiat/Abarth can't wriggle out of it, as far as I know.

I use a former BTCC technician who also looks after a couple of other Abarth 500s - he knows what he's doing, doesn't mind if I source parts for him to fit and doesn't demand instant payment before I get the keys back either.

Shop local!

Personally I wouldn't buy an Abarth without a full dealer history. Saving money now will loose you money come sale time.

Dealer or no dealer stamps. I would personally prefer to buy a one owner car from a person that clearly have maintained the car well.

I.e. I change my oil and filter at least once a year, the car is a 2012 and done 44.000 miles. Brake calipers cleaned and greased every spring etc. etc.

Better maintained and still way cheaper than following the service intervals.