When purchasing a home on a septic system, it is recommended to have the system pumped during the inspection period. While pumping the company will inspect the unit to make sure it flows correctly and is at safe levels. If there is an issue with the septic, that would be a warranted item that the seller would fix on a non as-is sale. Another thing to check into is to make sure it isn't in an area that is being transitioned to sewer. There is a large cost to do that upgrade. It is upwards of $11,000. One example of a neighborhood that is transitioning is Killearn Lakes. If there is a large septic repair to be done, it is not allowed and they will force you to hook into the sewer. As your realtor, I would help you look into these issues and have a septic pumping ordered by a licensed company.