I have bought a car through a member on IDO and it worked out smooth. I have also bought and sold a handful of cars on craigslist and marketplace over the years. When dealing with large amounts of money from a stranger I would only accept cashiers checks and sometimes go with them to the bank to get the check. Good to go to the DMV to to know the title gets transferred correctly. It is nice to be able to vet people you are dealing with through marketplace.
I still use craigslist more as a search tool because you can create saved searches for items and really narrow down what you are looking for and it will send you an email when something gets posted that meets your criteria.
If anyone has a used Toyota Sienna minivan they are looking to sell, depending on the year and millage I would be interested in upgrading our current one.