Ipsos is a funny name for one of the oldest and largest global market research companies. They were founded in 1975 and if you follow US politics, you'll recognize them partnering often with Reuters to produce approval surveys of Congress, the President, and other notable figures. They're headquartered in Paris, France and publicly traded on the Paris Stock Exchange. They have revenues of over a billion dollars – Ipsos i-Say is just a small piece of their business.
It’s a very well-known scam. You cash the check, then they ask you to either wire some of that money back to them as some sort of fee or buy something for them and send the item to them. So, you deposit the check, then wire some cash to them thinking that the check you just deposited will cover that. A few days later, after you already send them the money, the check will bounce and the money you send to them will come out of your own account.