I'm no expert, but I have purchased and sold a few things on CL.
Meet in person to do the sale. Assume that the person doesn't exist if you don't see them face to face. On large ticket items or vehicles with a title, meet at a local bank, car dealer, or title store to finalize the deal. Don't simply sign the title and hand it over to the buyer. Make sure that it is properly transferred according to the policy of your state. The last vehicle I purchased on CL was an ATV and the entire Notary bill was less than $30 for them to properly process the paperwork etc. Also, have them witness the transfer of funds if it is cash or if a check, do the process through a bank. One time, I was with a friend of mine when he purchased a truck out of state. The seller arranged with a bank to verify the check, title transfer, etc. all in one stop. It takes a little extra time, but for the small fee it costs, it is worth avoiding the possibility of fraud.
I agree with the above. Don't meet anyone alone or at your home. I usually have at least one other person with me as well as a personal protection device if you know what I mean.