Wait are you also sending to M via WU also?
I process WU transactions at my job. In general you should be really careful about sending money through it, as soon as it's picked up, WU (and us WU agents) cannot do anything about it.
If A is unable to pick up money even though all his info adds up, there's a chance that he might be blacklisted or otherwise blocked by the WU system (or the WU agent he goes to is refusing the transaction). Sometimes if someone makes a lot of suspicious transactions, receives lots of money from random people, is reported for fraud/scamming, or uses multiple IDs, they will get blocked by WU and unable to complete any transactions.
This is a really weird way to go about things... in the first place WU needs to see A or M's ID and write down all the info (ID number, birthdate, type and origin, etc) before they can pick up amounts over ~$100. Why would they expose themselves like that while doing illegal transactions for drug trafficking? Depending on the country they asked you to send to, and your own location, the WU system might be even more sensitive to these kinds of suspicious transactions.
It seems like A is a flake... if you're comfortable with the darknet why not try C? At least he does it through escrow, so he doesn't get the BTC until the product is sent out. There's still risk ofc, but wayyyy less risk than sending through WU, never getting your product, and being out more than 500 bucks.