b is cheap and to the point, Also it's easy to set up an appointment. call the local arb association and you can get 3 qualified to pick from. Court would be the next step, to collect.
Also, you have to look at it from my point... every seller wants more, every buyer wants it cheaper. both sides after 3 or 4 days get buyer's/seller's remorse. it's a fucking nightmare sometimes, I've seen fights break out at the closing table over 1 fucking key IE: it was a medco key, cost $25. and the seller wanted the buyer to pay for the second copy, and that's when I pulled out the listing contract and said " no, it's 2 main keys, you signed here remember ", and at the closing table is where people will try to screw you over ( both the seller and buyer ) that's why I never schedule both parties at the same time.
Also, do you want to take your client to public court, great reputation to have. No, Arb is always private and usually never even get's that far, good people realise the error and fix the problem.