It depends on the office. There is no requirement for a bill of sale, one of the forms you sign is a sales tax declaration, which IS required. The MOT requires the vehicle permit portion of the ownership signed to transfer ownership
I used to go to the franchise office at the HiPoint mall, that moved to Dixie/Dundas. Most of the clerks recognized me.
If I was registering anything more than 15-20 years old, they would insist on an appraisal. Not just me, everyone I know would be asked for an appraisal. No problem, I got a guy that will write anything I want for $50.
Now I go to the Lindsay MOT office. First old bike I registered, I brought an appraisal. The nice lady had no interest in even looking at it. When I asked why not, as it was REQUIRED at the Mississauga office. Nice lady says they are not REQUIRED, and tells me the clerks are instructed that IF they think the customer is trying to pull a fast one (that's us) they're to ask for an appraisal, and even went and dug up the memo and gave me a copy.
... so the Mississauga office was just covering their ***** by requiring an appraisal, JUST IN CASE.
I'm in the Lindsay office often enough there is couple of clerks that recognize me and I have never been asked for a bill of sale, so the price is $500... it's ALWAYS $500. The last time I was there, the clerk took my paperwork, and pushed the tax declaration at me to sign, already filled out for $500. I hadn't said a word.