In addition to the points already made, I'd add that the better tents are shaped in such a way as to keep the fabric taut which means that it doesn't flap nearly as much when the wind blows. Makes for a more comfortable night's sleep and also reduces the chance of the fabric or seams failing as a result of the repeated flapping.

I'll second the comment about REI's customer service. Bought a tent from them 25 years ago and recently had a problem with the end piece on one of the poles. No longer have any receipt or other proof of purchase but when I took it into the nearest REI store they quickly repaired it free of charge.