Hello chaps
The easy answer is this...
Your average car seat is going to be made from a synthetic material and very hard wearing, 9/10 times you can simply dry vac and apply a micro spitter such as SPM... agitate well and rinse.
For real mingers you can hit them a little harder using something like Shockwave, just remember to add an acidic product to the rinse tank.
The key to avoiding over wetting is applying just enough pre spray and agitate very well, using a tool such as the CFR will ensure the driest extraction results...
Once you have extracted, towel off the seats and start the engine... set the vents to the lowest position (floor) and increase the temp to max, leave the rear windows open just a fraction and close the doors...
Just remember to cover the centre console with a towel to protect from over spray