The answers here are all correct. This is 100% scam, beyond any reasonable doubt. Don't fall for it. However, I felt it valuable to explain what would happen were you to fall for this. It's not all that hard to understand, but it involves understanding some of the time delays that exist in modern banking today.
The most important thing to understand is that depositing a check does not actually put dollars in your account, even though it appears to. A check is not legal tender for debts public and private. It's a piece of paper known as a "bill of exchange." It's an authorization for a payee (you), to request that their bank pay you the amount on the check. A transaction made with a check does not actually draw to a close until your bank and their bank communicate and cause the actual transfer of funds to take place. This process is called "clearing" the check.
Despite living in the modern times, this process is slow. It can take 7-10 days to clear a check (especially if it is an international bank). This is not good for the banking business. You can imagine how difficult it would be to tell a poor client, who is living paycheck to paycheck, that he can't have his pay until the check clears a week later. Banks have an interest in hiding this annoying feature of the modern banking system, so they do. When you deposit a check, the bank will typically advance you the money (an interest free loan, in effect) while the check "floats" (i.e. until it clears). This creates the illusion that the money is actually in your account for most intents and purposes. (presumably a bank would distinguish between the floating check and a cleared check if you tried to close out your account, but otherwise it looks and feels like the money is in your hands).
Of course, if the check is dishonored (because the payer had insufficient funds, or the account simply did not exist), your bank will not get the money. At this moment, they will cancel any advances you received and notify you that the check bounced. Again, this happens 7-10 days later.
The general pattern of this scam is that they will pay you by a method which clears slowly, like a check. They will then ask you to withdraw the money using a faster clearing method (like a wire transfer or withdrawing the cash). Typically they will be encouraging you to move quickly (they are on a timetable... when their check bounces, the game is up!) At this time, it will appear as though the account has a positive balance, but in fact it has a negative balance plus an advance on the check. This looks great until 7-10 days later, when the check bounces. At that time, the bank will cancel the advance, and reality will set in. You will now have an open bank account, legally opened by you in your own name, which is deeply in debt. Meanwhile, the scammer walks away with all the money that you sent them (which cleared quickly).
There are many variants which can hide the details. Some can play games with check kiting to try to make your first check clear (then try to rope you in for a more painful hit). Some will change the instruments they use (checks are the easy ones, so they're simply most common). Don't try to think "maybe this one is legit." These scammers literally make a living off of making shady transactions look legit.
Things I would recommend looking out for:
- The scammers will ask for a bank account in your name. It might be your existing bank account (Danger! Danger!), in which case they can wipe out your entire life savings, or it may be a new account they recommend you create (they may pick a bank that they know isn't very good at watching out for these scams). However, the end results is always the same. You end up with a bank account which you opened up in your name, bled deeply into the red by the scammers. You now own whatever debts they racked up (and they're really creative in ways to do this). Because it's in your name and you actively caused every transaction to occur, not only do you have few resources to get your money back, but you are, in fact, committing fraud and you can get in trouble for it!
- The scammer will try to manipulate your sense of urgency. In general, they will try to make you act very quickly, while they themselves may act quickly or slowly depending on what story they're trying to sell. Nigerian 419 scams (a common variant of this) are known for trying to create the illusion of a payday transfer that's in limbo, and just needs a few more dollars to make it happen. Don't believe them, the payday doesn't exist.
- The scammer's story sounds obtuse. One common trend with them is a story where for some really odd reason, they have a transaction they need to make, but cannot make it themselves. For some reason, it needs to go through a third party. There are very few cases where this is legal, and I can't think of any cases where they're reasonable. If, for some reason, they need some third party they've never met to make the transaction for you, this should be flagged as suspicious always!
- Scammers make a living off of this. They are creative, and they are persistent. I've listed a lot of common traits of their scams here. Do not assume that they will abide by these as rules. Right now, most of the scams show these traits because that's where the money is. If people get better at spotting their scams, they will move to scams that you didn't expect. Don't assume that, just because a particular individual isn't doing anything on my little bulleted list here, that they aren't a scammer. These are good things to look out for, but use common sense. If it smells funny, get out!