Before jumping to the conclusion its the bearing, be certain that is the source. My wifes wheelchair had a squeak that matched the wheel speed, and it seemed reasonable the bearing may to be blame, lubrication didn't work because it wasn't the roller bearing, it was the actually the axle shaft, which had a quick release system to allow the wheels to be removed. Not necessarily applicable to the mobility scooter, but it pays to keep an open mind.
Generally if a bearing does need to be replaced, any competent mechanical DIYer should be ok, so unless there is still a manufacturers warranty in force it doesn't need to be done by the shop.