Toyota Repair: Fuel Gauge Readings, gauge reading, gauge readings

Question
2010 Toyota Rav4 Sport, 2wd V-6 –
The fuel gauge appears to be faulty or mis-calibrated.   When the gauge reads empty and the fuel  light comes on, I can never get more than 12 gallons of fuel in at the pump.  So, there is at least 4 gallons left in the tank when showing empty.
The local Toyota dealership that my wife took it to for routine service told her she had probably overfilled the tank and got gas in the canister and ruined the canister.  Didn’t run any tests, just advised her that this was likely the problem and they would have to replace the canister.   I told her to get out of there as fast she could because they were obviously trying to take advantage of her.  So my question is can a problem with the evap canister cause a faulty fuel gauge reading?  Is there a way to calibrate the gauge?

Answer
Hello, I doubt if the canister is the problem, unless the check engine light is on and the canister is saturated with fuel due to a malfunction the canister is not the problem, it's more likely that the fuel sending unit in the tank needs to be replaced, the dealer you are going to seems to not be interested in checking and testing problems they just want to replace things and hope it fixed it. The  fuel level sytem can not be calibrated on this model.