I was going to offer to have the testing done but tell the tenant that if the results show no harmful mold, the cost would come out of her security deposit.

Small Deposit !!!

 #3 Allowing a tenant to pay a deposit via a non-profit.  

bank.. which bank do you use for receiving your rents and holding security deposits.

Their service, just like any other, is not without drawbacks. (1) I'm not a big fan of their rent collection b/c they make you deposit it into their account and I'm not overly comfortable with an unregulated entity having any say over my money. 

For example you hold on to the land while they get plans approved and they pay a premium with a non-refundable deposit.

I rented an apartment and the property management company added 6 k in move out charges to repaint the entire interior of the home due to minor marks (didnt give back 4 k security deposit and charged 2 k on top).

If he is still there, you may want to try a little game about returning his security deposit/following the law.

So I'm not sure how that would affect this option but it might but this option costs $0 in capital to you - unless the contractor wants like a 10k deposit or something.

With the lease to purchase the seller more than likely would ask for a deposit that can be applied toward the down payment when the actual sales take place or the seller can "finance" a certain portion of the down payment.