For as long as I can remember AMEX fees to the merchant were exorbitant so I discouraged or outright refused to take the card.  Reviewing my CC processing fees  I find AMEX is now pretty much in line with all the others.  While it is inevitable that some car repairs will be expensive and we can only do so much about that, no need to be inflexible about method of payment!  Bring your AMEX card!