Autotrader has always got me a sale when used, though my ED30 sold on here without an official advert.
I would buy a pay'n'go SIM if putting your number online, you can always give the buyer your usual number, but keeps it away from search engine spiders etc.
my mate must get ten PPI type calls a day as he has no qualms sticking his number on forums, Gumtree, ebay ads.