As stated, get as much information about the person and product that you can. For example, check feedback, ask for references from people they have dealt with that have good feedback that will vouch for them if feedback their is low or zero, cell phone number, pictures of product and ALL negative attributes against it (base gouges, edge cracks, stain on clothing/outerwear, etc.), pics with username and date. The more you know, the better your deal will be. A good NSer/seller will be happy to oblige to these requests because they know how thing go. If they give you trouble with asking a lot of questions or requesting more info/pics, they probably aren't someone you want to do a transaction with anyway.
That made my hand get a brain freeze
Do you need a tissue after that steeze?
"People were asking me what size my Jesters were too.
YOU GUYS ARE REEEETTTAAARRRDDDEEEDDDDD!!!!!!! YOU MOUNT THEM TO ANY BOOT YOU LIKE!
GOD DAMMITTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT IM GONNA KILL SOME KITTIES!
And if you're retarded enough not to know these have a max DIN of 16, there is this magical invention called, wait for it......... WWW.GOOGLE.FUCKINGDOTCOM