The toilet quietly refilling itself every few minutes is the problem we find most often, and the one that costs the most to ignore.
The quiet running one
If you can hear water trickling into the bowl between flushes, the flapper or fill valve has stopped sealing. Inexpensive part, quick visit, and it may be adding a surprising amount to your bill each month.
If the toilet rocks
Any movement means the seal underneath has failed and water is getting into the floor rather than down the drain. In older James Island homes with wooden subfloors, and damp underneath already, that leads to rot faster than it would elsewhere.
Older flanges
Homes from the fifties and sixties often have a cast iron flange under the toilet that has corroded. Fitting a new toilet without dealing with that just brings the same problem back, so we check it while we are there.
Repair or replace
Most toilets are worth repairing. If yours is original, needing attention regularly and using far more water per flush than a modern one, replacing usually pays for itself.