The seals help so that the air doesn't leak through the zipper. Seals usually don't have a problem until way past the warranty period. The most common problem is that they crack and split over time. Usually people that buy the used chambers, mostly the ones older than 10 years, can have this problem.
I wouldn't worry about the seals being and issue when buying a new chamber. The only thing is that some of the hyperbaric seals are behind 3 zippers versus 2 zippers. Some you gotta massage more than others to lay flat. When pressure is on the seal when inflated and the seal is not perfectly flat, this lowers the integrity of the seal and is probably why they crack over time. It's kinda like bending a paper clip. Sooner or later it will bend and break.
Notice: Some hyperbaric chambers do not have any seals between the zippers and make it much easier to zip up and get into the chamber. There is a choice to make before buying a chamber. do you want a rubber gasket between the zippers or do you want the ones with no gasket with an airtight zipper.
Are the seams welded or sewn? This is the first question I would ask.
What seams last the longest? Knowing the answer to the first question will answers this.
Is the Head, Feet, Zipper, & window portions of the chamber single, double, or triple stitched or welded.
Will the cold or heat bother one seam more. Some you can leave in the sun and others its not so cool
Note: If you see a used chamber that has yellowed, (oxidized) this is usually due to lots of sun or ozone. This is cosmetic. The hyperbaric chamber will still function.