I would be concerned on two counts.

1) If it's running on four worn tyres, I'd be worried about the rest of the car's upkeep – not replacing tyres is a sure sign other things have been neglected. That could be a bigger concern on a low mileage car like this because low miles tend to indicate a car has been used for lots of short journeys that are harder on the mechanicals.

2) I'd also have concerns about buying a car from a dealer who is willing to sell a car with advisories on all four tyres and whose solution is to offer you a set of mismatched replacements. In an ideal world, a car should have four matching tyres to ensure it handles predictably and a dealer should know this.

I'd push to see the full service history (sounds like you have done this already), get four matching tyres fitted by the dealer and double check reviews of the business to gauge its after-sales support.