If a generator technician has a good background, it will be easy to find out with a quick visit online search, but also check out this page's list of pros with their grades. Also, ask your technician for referrals from customers they've worked with before.
While some home generators still use gasoline, most generators run on propane or natural gas instead. Check your user's manual or call the manufacturer for more details.
While some generator repair experts may be able to give you an accurate idea of how much their services will cost over the phone, it's often necessary to physically examine a generator to understand what's wrong. Ask a repair company you're considering working with if they provide free in-home consultations, and then ask them which parts are broken when the consultation has concluded.
Some parts, such as transfer switches, may cost less than $100 to replace, but expensive parts like stators may cost over $1,000.