The toilet might look clean but it’s important to check under the rim where dirt can build up out of sight. A good way to check it is to wet some toilet paper and rub it under the rim (rubber gloves recommended).. You’ll see if there’s a black residue there. If so, have a grout brush on hand, wet the bristles and pour either cleanser or a thick toilet bowl cleaner on the bristles. then rub it around under there. Flush, while rubbing the brush under the rim again. Do this a couple of times and it should come clean.
For caked on dirt, use a pumice stone.