I think you are providing a better and more accurate service if you do it yourself. The electret cannisters, if that's what you are thinking of using are easily screwed up by dropping which happens how many times a day if you mail them out? Lots.
Also, I find generally a loss of 1 point per day just sitting in a drawer, so if you leave them in your car for a few days your customer may be getting a poor test.
I read the cannisters before every test and after I pick them up.
Brokers love the fast service and I love making sure my client has the most accurate test possible.
WIN WIN WIN. The third wins for the 125.00 per test