Just to come back to you about what MCN does/doesn't do. Firstly, yes we do sell a lot of bikes (see here for some testimonials).
We are also very aware of these scams, and actively publicize these scams to the seller on both the confirmation email we send out to sellers and on this page: We also forward these to trading standards, but as the scammers invariably live outside of the UK they are very limited in their actions.
In respect of stopping these scammers, we obviously try to block known scammers from contacting our advertisers, which we do work on (we have a blocked list of 450+ scam emails!!) - however as scammers change email addresses and/or IP locations it's impossible to cut these down totally without manually checking every response from them. We don't do this as we would need to dramatically increase the price of advertising in order to manually check each response, so this isn't a viable option - we are however already working on a more sophisticated automatic scam catcher which will be introduced in the next month or so.
As a general rule, if someone doesn’t ask specific questions about your bike, is happy to buy it unseen at full asking price, or wants to pay for it via an unusual or unwarranted way, please simply ignore.
I'd also like to re-iterate greengeeky's point that not all foreign buyers are dodgy. We're aware of a lot of dealers in Belgium, Netherlands and Germany who are keen to buy private English bikes, but the buyer's knowledge of the bikes in question and willingness to meet in person seperate these approaches from the "Dear friend I am, so lucky to find your bike for sale, please accept this cheque for more than the asking price and pay my shipping company the remainder..." style scams.
I hope this info helps. Sadly scammers do go through all online classified sites concentrating on high-value items, but please be assured that we're not blind to this, and are working on ever better methods to defeat these idiots.
If you have further questions, please feel free to email me (firstname.lastname@example.org) or drop me a pm.