Two days to order and pay is perfect.
Must they show proof of order and estimated ETA for products purchased within this time? If not, I think you should require it. Details in the chain of custody can reveal if there is any foul play.
Additionally, consider having them show proof, with date, of when they received products.
There should be a time set on mailing products to lab as well. Maybe within 24hrs after receiving it? 48hrs? And again, they should show proof when, how, and to who it was shipped to.
Do trusted buyers have to wait for funds from the program or do they get reimbursed?
If they are reimbursed, the reimbursement should only come if the time allotted for each phase is confirmed with proof. Kinda harsh sounding maybe but something like that creates incentive to follow a consistent protocol that only benefits the programs legitimacy as a whole.