How do you to figure cash flow profit from a rental property?

[Tony Marcelle]

I have an investor sending me properties everyday in my inbox. They are rentals with property manager and tenants already in place paying rent. One of the houses is selling for $25,000 that is rented at $650 per month. The investor said the only expense the buyer of this house pays is the closing costs. The property manager charges 10% of rental income. I am looking for a private lender. The renter pays taxes and utilities. I assume I take out whatever interest rate the private lender will charge from the rental income. Any other costs I need to be aware of?