This has just happened to me...fortunately I was aware and did nothing about it. I informed the Bank who are following this and others with the fraud sqaud.
Most of you will be already aware of the cheque scam follow products advertised, but for those who are not, please read the following warning which I have copied from Organfax.

SCAMS ON CLASSIFIED ADS SECTION
As mentioned before on our News Page, these attempts at money laundering continue to come in and we are receiving quite a few concerned comments. Unfortunately, there is nothing we can do about this, short of shutting down our Classified Ads, which would be rather extreme. It wouldn't stop it happening to others, too.
The police are aware of these scams and say there is little or nothing they can do about them and simply suggest that advertisers be vigilant and ignore any contact that does not appear to be genuine.

We quote below a couple of typical email approaches - just as received, with no corrections made to spelling etc. In each case the instrument mentioned is from a legitimately posted advertisement but the name of the enquirer varies. There are various email addresses given for response but these are obviously only temporary ones.

You may be interested to read an email just (Aug 2004) received by us on this subject ...

"I was recently emailed by some guy who wanted to buy my organ. After some correspondence I became very suspicious. Basically the guy lived in Belgium and wanted to buy the organ. He said he had a business colleague in the UK who owed him some money and he would have them send the cheque to me. Because what he was owed was more than the amount of the organ I should take the price of the organ from the amount and send the rest to his shipper via Western Union. I was obviously very cautious but thought, well, I will not part with anything until the money is in the bank, so I agreed.
The following day a cheque for £7200 arrived via UPS and drawn on a Bank of Scotland account. The value of the organ was for £3800 so I would be sending £3400 less the cost of sending to his shipper who would arrange collection. I emailed to say the cheque had arrived and he sent me an address I should wire the balance to. It was in Nigeria. Immediately alarm bells started going off so I took the cheque and copies of the emails to the bank who are at present checking it out. I then came back and did a search on Google and sure enough it seems that this whole thing is a fraud ...see http://www.data-wales.co.uk/nigwu.htm

"The important thing to know is that most banks will clear the cheque and the victim thinks everything is OK and sends the money. Then ten days later when it reaches the drawing bank it is found to be fake and the money is withdrawn by the bank from your account. You are the loser. The bank protect themselves with a small clause in the contract details."
So - be on your guard if you advertise ... either on Organfax or anywhere else on the 'net, as this is not unique to the Organfax site

I have put ads on a free site, where I have
received the same type of money laundering scam. What's usually a giveaway is that
the weasel has very poor English, and really
doesn't ask any specific questions that a
real buyer would ask. It's more like " I
am going to buy your...., but a friend in
America owes me money, so he will send you
a check for $2000, take what you want for
your item,and wire me the balance, and I will use my private mail service to pick the item up. They usually use names that start
with Dr.
I wish we could use an FBI address where
they could send these fake checks, and then
send them a letter, to go f... themselves
because we decided to keep all the money.