Tell me what you've learned buying yarn on the wild wild web

Hello, I have been returned to crochet for only about 5 years now, and I consider myself intermediate in skill. The yarnscape has changed a lot since I was a kid, both because of the reduction in brick and mortar stores, but also because I am now disabled and cannot hop in my car and drive 2 hours to reach the best shops! I am used to being able to speak with shop employees who are knowledgeable crafters themselves and often had personal experience with the yarns they sell. After a recent disappointing experience where a couple of gifts I made ended up with a very short lifespan due to my selecting subpar yarn online, I figured I'd ask everyone what they've learned for themselves--besides the obvious start of reading reviews, of course!

What do you look for in a description? What are some warning signs you've learned to watch out for? What can you glean from pictures? Does what you look at while selecting yarns vary by project type? For example, I generally think of a project, and then shop for yarn. Do those who buy yarn first, and then match a project to it, have an easier time with web experiences? Lastly, what factors do you consider on whether you want to take a loss on the return shipping, or to stash it?