Is it fair to negotiate ...

[rexcramer]

One man's opinion, 10.5k sounds high for a 99 with 55k on it. It would have to be in near perfect condition, one owner with a verifiable/documented maintenance history to warrant that price. (Based on my California experience)

Subtract in the fact that it has been tweaked in an accident. (Big Subtraction) Unless you are a really experienced home mechanic, I think you must pay an experienced Porsche Boxster Tech to do a thorough inspection of the car. If the current owner balks at that idea then walk. It will cost you $300+/- but, it will tell you the truth regarding the health of the car. All the forum can offer is conjecture.

Keep looking. Convertible selling season starts this time of year in the NE?

To answer your original question, Yes, negotiate your back side off.