I imagine scam contracts is a problem that occurs worldwide, so while my personal experience with this was in Sweden, my warning is to any student thinking of studying overseas. My warning is about fake wage, employment certificates, or contracts. In general, domestic students aren’t going to be stung by these kind of cons as they know the local system, they know their rights or who to speak to to find out their rights. Because foreign students don’t have the same knowledge, may have just spent their last $ moving across the world on a false promise, and have no networks to support them in their new country, they are the most at risk of being conned. Because of this vulnerability some unscrupulous supervisors have been known to send fake employment certificates promising e.g. higher wages than will actually be paid. To avoid this happening to you, you can check with (your future?) university HR, finance, and/or the local student union about what are the accepted normal wages and conditions for a doctoral student at the university you are considering. Do this before you accept the contract, and most definitely before you move.
For Uppsala University basic information on wages is provided by the studentkår: http://www.uppsalastudentkar.se/doktorand/phd-handbook/funding-and-financial-support but each faculty and department will have a more detailed description of their contracts. General guide for doctoral funding in Sweden: http://www.doktorandhandboken.nu/engelska/handbookforpostgraduatestudents/funding.4.24cc9d95134182bfa4a8000107.html
If you have been offered a contract that is in any way different to that typically offered local students be very very cautious about accepting. Be vary cautious about signing anything that looks official or mentions income. Once you sign papers so you can get paid the wages you have earned it is seen as acceptance of the real contract rather than the fake one you were sent and you can no longer demand the wage you were promised. The things is, if you know all this before you move, before you sign papers to get paid, you can get it fixed by notifying HR, finance, head of department, student unions etc and the scamming supervisor will be made to give you the correct contract or the correct wage. In this way the Swedish universities are really good as they have very strictly observed rules about wages and conditions. It also means you will know what your income will be before you move or even decide if you will move. These problems sadly arise as there is no control over scam-artist supervisors and their behavior, it is up to you to check. Just because the Swedish system is amazingly equitable does not mean all who work there are. Just because a certificate has an official university letter-head does not mean it is officially sanctioned by the university!!!
SO whatever you do, DO NOT SIGN any contract that is different to what you were promised… even if it means becoming homeless, or going hungry, or getting kicked out of the country (if you have no proof of wage/contract then you have no residence permit). Once you sign, you have no ability to change your contract. So DON’T sign. But better yet, heed this warning and find out your rights and employment conditions before you decide to take that offer that is too good to be true.