Ontario, Canada process (went through this last fall):
+1 on don't buy anything you think is stolen, cops or karma will catch up with you. It's a big red flag if no title exists so find out as much as you can about why this is the case. If it doesn't feel right it probably isn't.
It's legal here to sell a (non-stolen) bike "for parts" (no title or intention to register). I was looking for a restoration candidate and bought a "parts" bike from a guy that had also bought it for parts (so no title), but ended up not using much from it and it sat with him for ten years. I talked to PO at length and believed what he was telling me about his knowledge of the bike's history, and knew where the guy lived so could turn the heat on if anything wasn't true, but even so it's still a gamble. I obtained registration first, before doing anything else.
The steps and costs:
get a receipt from the PO with their name, signature, address, purchase date, amount, and bike model/VIN (free, essential. IF PO WON"T SIGN A RECEIPT, WALK AWAY)
get an affidavit stating your name address, PO name address, bike VIN and model, circumstances of purchase, and saying "I am making this statement for purposes of obtaining registration and no other improper reason". (cost approx $80-100, I wrote it myself and got a favour from our company lawyer to notarize it)
go to Driver and Vehicle office and pay for a Used Vehicle Info Package (the indirect Ontario money grab which runs the VIN to show ownership history, technically the PO's responsibility but in actuality always falls to purchaser, approx 25$) If the bike is stolen, this step will/should reveal it, so hold your breath and hope the story you were told by PO is true. In my case the VIN didn't show up in the system, this means the bike was not registered in Ontario previously, and had not been registered as stolen). Most challenging part of this step was that the lack of a now-standard 14-digit VIN confused the computer and the staff, but thanks to my genius suggestion ("add some zeroes to it to make it 14 digits") we were on our way.
Paid tax on the purchase price - (this would be the direct Ontario gov't grab)
Paid for the cost of a registration (I think $74, grab grab grab)
With the receipt and affidavit in hand, the actual visit to the Vehicles office took 15 minutes, they (and I) were satisfied the bike was clean, and I walked out with the all-important registration document.