I'd go the opposite direction from Ron. Keep the fee low enough to cover your time and then have a bulletproof contract. This is not engineering, you should not be liable for anything other than your $520 fee. Limit your liability to the fee charged. Warranty nothing. Use clear contract language that this is a non-destructive, visual inspection that is not guaranteed to find any defects, hidden or visible. Etc.
My old boss did home inspections and was quite good at them. Generally caught everything. One homeowner bought a house and did some renovation (probably to flip the house or something), discovered rotting sills. Claimed it cost him $30,000 to fix. Knew they were in the wrong but still went after my old boss. Made a complaint with the state PE board, lawsuits all around, complaints wherever he could post them, etc. Boss man had a good contract, refunded the fee for inspection but still had to fight the lawsuits and respond to queries from the board. Owner tried to claim things that weren't true. In the end it went away but not before boss man had his name dragged through the mud a bit and likely his E&O insurance had to fight the lawsuits for a while.
It can make money but make sure you're covered.
Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)