Nope...this isn't trickery. This is one way to make sure that the transactions all line up.
Most sellers don't want to tie themselves to a deal if it's dependant on a property sale that isn't on the market. There are just too many variables in play. You CAN go on the market with the stipulation that you first need to find a new place to purchase. If that doesn't happen, then your house isn't for sale. I've done this a few times through the years. When an offer comes in on your place, they usually build in a clause giving you a limited amount of time to purchase, or they can get out without penalty.
The upside is that you stay in control, and don't end up owning more houses than you can afford. (Actually, the mortgage company would prevent that by not issuing a mortgage commitment to buy if your current house wasn't sold). The downside is that some potential buyers for your house might not be interested in waiting for you to find something else. This could limit your buyer pool.