If they ignore basic questions or reply with copy pasted text, I become suspicious. It saves a lot of trial and error for everyone else. I also check if the store explains how to measure PD and frame size clearly. If tracking never updates for weeks, I start to worry about the order. Now I am more careful with impulse buys and limited time offers. Even big and famous brands sometimes send generic replies that are not very helpful.
Sometimes I still make mistakes with size, so a friendly exchange policy is very helpful. In the past I have wasted money on items that looked good in photos but felt cheap in real life. Very thin fabric may be fine for summer but often looks cheap and becomes see through. Many times I avoided a bad purchase just by reading a few careful comments. I also pay attention to return policy and customer service response time.