Can I record a conversation with someone face-to-face without their knowledge in Michigan? (Not Phone Calls)?

I started allowed my friend to purchase from my business on a credit line. At first, the credit line was always paid on time. However, over time, it's grown to about $6000, and hasn't been paid on for some time now. I should have always gotten a signature for each purchase, however I didn't since things had been going smoothly. (OOPS!) I don't think a court would take my business's records as proof of transactions without signatures (maybe I'm wrong...) The only way I can think of getting proof he acknowledges the transactions is to tape record a face-to-face conversation about the balance. I'm sure he wouldn't be willing to talk about it if he knew he was being recorded. Would doing so be legal in Michigan and admissible in Michigan courts? I know recording over the phone complicates the legality, so I would do it in person instead of over the phone. I've had some "heart-to-heart I need the money" conversations. I'm going to have another soon but I don't think it will help.