I have done a few recorded calls and like Ivan mentioned, it is very easy through iSecretShop.
While I have only done one shop with them, they quickly processed my shop. Service thus far has been great!
Great question and looks like some sound advice in this thread. I would certain speak with a qualified accountant or the IRS in this instance.
I performed a mystery shop where your reimbursement was exactly what you paid for the meal. I looked at it as a free meal but am less inclined to doing that in the future. I would prefer the difference between fee and reimbursement to be greater than the cost of the meal.