Rust Stain Removal:
Rust stains can be challenging to remove, and their removal may vary depending on the source of the rust and the surface affected. Groundwater is a common source of rust, and it can lead to stains on surfaces like concrete, brick, or stucco. In these cases, effective rust removal can be achieved using the appropriate chemical cleaning agent.
Unfortunately second scenario is battery acid on concrete (did you see this under the golf cart?) this is actually an acid burn and most likely a permanent scar on the surface and the best we will be able to do is lighten the stain.
Third case scenario rust stain that is extremely difficult to remove is fertilizer, you will see little rust dots near the lawn areas in this situation the best possible outcome would be to lighten the stain
Bottom line is im not going to lie to you and say everything will be great, I've seen this many times and I don't tell you what you want to hear just to get your job. You will know my limitations up front..