One thing I've only just recently learned... many municipalities forbid commercial delivery (I presume of a certain vehicle size, the otherwise is okay to drive down that road) in residential areas. You would need a special exemption permit to allow a large vehicle to make a delivery to your address. This has become somewhat more common in the last year with everyone starting a work-from-home business type thing.expect to pay at least $100 extra
Another common thing, in areas that are being gentrified, many municipalities will take old neighborhoods that were originally zoned residential only, and instead zone them as dual-use resi-comm with the idea that over the next 20 years businesses will be buying those homes as they come up on the market, and putting businesses in instead of homes. This happens by municipal decree without making any upgrades to the streets or buildings whatsoever.
I don't think it has anything to do with a liftgate, though that may be an additional concern. Many businesses don't have loading docks. Random examples: 7-11s usually don't, streetside pubs usually don't, most fast food places don't, most motels don't, etc. If their issue was "must have loading dock" they would specify that separately, not word it vaguely as "commercial address".
Sounds to me like it's just to rule out annoying one-off residential customers. Depends how thoroughly they're checking. Most places you have a sole proprietarship be personal decree, i.e. You have a business because you say you do, and it's no different than any other income you earn as a person. Forming a corporation often makes sense for isolation of liability, but that's only a general rule. There's no thing that makes you a business. Tomorrow you're "Mike's Custom Conversions", no registered trade name, no paperwork, and you're a business. You might need a business license to operate in your municipality, but that's generally only if you're selling things so no one there will care. The seller may street view you and see you're a residence, and you can just claim your garage is your business. Then they may want to see your business license. Licenses are usually pretty cheap. You could try saying in your area, you don't need one until you have services to sell, so you're holding off until next year and only designing right now.
It all comes down to what they want and why. Solve the right problem.