Learn French: Le garagiste risque d'abîmer la carrosserie. - The mechanic risks damaging the bodywork.

The verb risquer (to risk) requires the preposition de when it is followed by another verb in the infinitive. Because abîmer starts with a vowel, de drops its e and becomes d'. In English, we say "risks damaging" with an -ing word, but French always uses risquer de + infinitive.

Does garagiste just mean the garage itself?

No, a garage is the building or workshop. A garagiste is the person who works there, like a mechanic or garage owner. The suffix -iste often indicates a profession in French, similar to "-ist" in English words like "dentist" or "artist".

Could I use casser instead of abîmer to say he damages the car?

You could, but it changes the meaning. Abîmer means to damage, ruin, or spoil something, which is perfect for scratching paint or denting metal. Casser strictly means to break or shatter something. For a car's bodywork (la carrosserie), abîmer is the most natural choice.

If we already know we are talking about the bodywork, how would I say "The mechanic risks damaging IT"?