I just sold my bike on C/L. Went thru all the same BS (VIN check requests, third party shipper, cashiers check for twice my asking price, etc.) most communication stops when I tell them to meet me at the address shown on my advert, it's the Benbrook PD and they have a Safe Trading area under video surveillance. The guy that actually bought it had me worried at first, when he said the ATM broke and changed the meet up to the next day at 8, then delayed that because the bank wasn't open yet, but I took a deep breathe and told him to text when he was on his way. He did, and we met at the PD. He handed me cash before even asking for a test ride. Then he asked me to ride it home for him, gave me his address and said "I'll meet you there". I must have a trustworthy face because I had the bike, and the Title, And the cash! Anyway it all worked out great, we chatted a lot on the drive back to the PD, nice guy even though he's not from around here (well, neither am I). We might even get a new TWT member out of this!
Bottom line is C/L works, just go slow and be careful, ignore the obvious scammers, if you don't get that warm fuzzy feeling - stop the process. It might take a little time but the right deal will come through. For what it's worth - I have had the same problems with eBay and CycleTrader.
Scammers and Spammers - Shoot 'em all and let God sort it out!