Airwalk. If the scraping is not a representative of the whole pill then there's no way of telling whats in it, and Marquis Reagent will be useless. Binders and fillers do not react with the reagent so if you react a smaller amount of MDxA, it would stand to reason that the reaction proceeds slower.
I've been in this dealer situation before. My friend scores for me and puts up the money, if he gets a rotten deal I can't exactly say 'I'm not buying them if they're shit.' It's a shit situation.
You could write down a list of good & bad pills from pillreports.com etc. Take it with you next time as a reference.