Everybody knows not to get sucked into those absurd Nigerian e-mail scams.

The scam goes like this: Some fellow in Nigeria just got a United Nations contract, but he needs to deposit the money in the United States for security. If you’ll deposit the money for him, then you’ll get 10 percent.

What people don’t know is the actual mechanism of the scam. It’s a mechanism that is being used much more astutely in many ways. Watch out. You could get scammed. I almost did.

The scam relies on a minor detail of banking that most people don’t understand. Most people think when the bank takes your deposit and credits your account, then the check is “cleared” and the bank guarantees it. But this is not so.

A bad check can take weeks to bounce. And when the bad check bounces, the bank will “unclear” your check, debit your account and expect you to make good on any missing funds in your account. Ouch.

The scams always involve sending a fake check or money order. You deposit it into your account and when it “clears,” you’re expected to wire a portion of the money somewhere else. Weeks later, the check bounces. By that time your customer and the wired money have disappeared. Then you get the call from your bank asking when you are going to deposit additional funds in your account to cover the wire transfer.

These scams typically show up when you are selling some big ticket item, in my case, an airplane.

The scammer will always send you more than the purchase price, with instructions to wire the money on to someone else. My fraudulent airplane purchaser was going to wire extra money for overseas shipping. I was to deposit the check and wire the shipping cost to the shipping company.

I received a very real looking money order from a prominent national bank. I deposited the money and, sure enough, the funds were available to me within 24 hours. That’s when I was supposed to wire several thousand dollars to a shipping company.

Fortunately, I was suspicious, so I called the bank whose name was on the money order to verify the check number. A few hours later, a bank official called me back and asked me to fax a copy of the check. The next morning, the bank called and advised me the check was a forgery.

Meanwhile, the “buyer” was desperately asking me why I had not wired the money to the shipping company. If I had done so, the check would have been returned for insufficient funds and my bank would have expected me to pay for the wire transfer myself.

To be sure, the signs were clear that the deal was amiss. The e-mail address of the buyer was a generic address. Be suspicious of buyers who use e-mail addresses with endings like gmail or yahoo. Such e-mails can’t be traced.

The buyer had a foreign accent and always called from a cell phone with blocked caller ID. Such cell phones can be bought at a store and discarded. They can’t be traced.

Never accept payment by check or money order. Make them wire the money. Never, ever accept a payment greater than the purchase price with instructions to wire money forward. These are always scams. In particular, never wire money overseas.

If there is any doubt, call the bank and make sure the check has really “cleared.” This is different from the funds being available. Just because the funds are available to you does not mean the bank has received the funds from the deposited check.

Of course, this is where no good deed goes unpunished. Or how government regulations can botch anything.

The government - looking after consumers - decided that banks were dragging their heels allowing customers access to their deposited funds. So the feds mandated that banks had to make funds deposited available to consumers within 24 hours of deposit.

To get this law passed, the feds had to allow banks to recoup any losses from any bad checks that later bounced.

The average consumer believes that the bank - being prudent - would never allow a customer access to funds unless the funds were rock solid. And this is true.

But the banks aren’t calling the shots. Federal law forces the banks to make the money available to you within a day. In essence, availability of funds has no bearing on a check being truly “cleared.”

These scams are increasingly common in the Internet age when many transactions occur in cyberspace. The same amazing technology that allows you to sell a used thingamajig to someone around the world, also allows a poor Bulgarian operating in his basement to scam thousands in a week. There’s a sucker born every minute. Ebay transactions are rife with these wiring scams.

Being a good citizen, I reported the fake money order to the FBI and the Secret Service. One dutiful agent actually called me back for details. I asked him if he wanted me to send him the check. He laughed, “I’ve got a pile of these scams two feet high on my desk. If you didn’t lose any money, don’t bother.”

I admit to goading my scammers by playing innocent, despite my suspicions. This at least gave me some cheap entertainment. I convinced them I was on the verge of wiring them thousands. It was hilarious to see their desperation rise as the wire transfer was coming - they thought - within minutes.

When I told the scammer there was something wrong with the check, he acted indignant and suggested I fax him a copy. “There must be something wrong. My client has a perfect reputation.”

It was finally time to pull the trigger. “This is just a scam. I’ve known it all along,” I boasted. ‘Click’ was the only response as the scammer moved on to the next sucker. Don’t let it be you.