I sold a set of 16" E46 wheels on Craigslist once. I had three 'buyers' contact me with similar questions like the OP experienced. Very annoying. The real buyer called and asked the right questions, told me what car he was going to put them on and showed up with the correct cash and no issues.
I then tried selling a computer on Craigslist and got all kinds of turkeys -- not one serious inquiry. I did get an offer to ship it to Nigeria, but I politely declined that one...