Money orders, cashier's checks, certified checks, draft orders - these are different things that are, in essence, the same for you. You can deposit them all just as you would any other check.
Money orders are issued by postal agencies (USPS, Western Union, Moneygram - the most common). Cashier's checks are issued by banks. Certified checks are issued by credit unions. Drafts are issued by government agencies.
In all these cases the issuer is on the hook, not the person giving them to you. For that reason they are sold for cash or some other way of guaranteed funds, and in any case the sale of the instrument is the transaction between the issuer and the buyer, not you.
The risk is with fraudulent checks. This is a very common scam over the internet - someone mails you a cashier's check and then asks for refund or money back under some pretense. It takes a while for the fraudulent checks to be identified as such and bounced, it may take weeks or even months.
This scam would rarely work in an in-person transaction using a traceable and easily retrievable asset like a car. If someone gives you a forged check for a car - they'd be pretty easy to find.
To be on the safe side you can agree with the buyer to meet at the bank and watch them buy the cashier's check that they'd then give to you in exchange for the title. I've actually done that once as a seller.
