I agreed to buy a very nice used car from someone, and I will be paying him a nice chunk of cash. What worries me is the title he showed me. It is signed and notarized. He says the car belongs to his mom who is very sick in the hospital and he had her sign the title so he can sell her car because she will not be able to drive. It sounds legit to me. How can I be sure this is her signature on the title ? What if by some miracle she is fine again and finds out her son sold the car without her permission ? Worse yet, what if he forged her signature to sell the car and keep the cash ? What is my due diligence here ? Is this title good as it is - signed and notarized ?

Assuming the notary isn't in cahoots with the seller, you are good to go. "
How can I be sure this is her signature on the title". Notary should have verified signiture before stamping. I know my wife never would notarize unless it was signed in front of her and with pictured ID. The name of the notary is on the stamped seal, check with them if you have questions.

Also in some states there is a separate form that the DMV (or other office) requires to be signed and notary if the seller is someone other than the owner.

Ask what hospital and check to see if she is actually in hospital.
Seldom does someone stay there for weeks.

Thank you guys so much ! You have been very helpful