A lot depends on how the cover was built. For instance it makes sense for us to match the quality of thread to quality of fabric. If we use a material that is warranted for five years then we should use a thread of a of a comparable quality. No thread manufacturer will warrant thread, but there are some threads that will withstand the sun better than others. The same goes for webbing that is used for straps and the quick-release fasteners.
Quality usually costs more.
But even if a seam is coming apart, it isn't the end of the cover. It can be repaired. Many cover manufacturers use Sunbrella, or will if you ask them to. Sunbrella is a woven acrylic canvas. It withstands the sun, and is breathable so it won't trap moisture.