Using unreliable web hosting will have a negative impact on your business sooner or later. It might be more disastrous if you chose to stick with a host just because you don’t want to be bothered with switching. It is well worth it in the long run and most web hosting companies will help transfer your site for free.
Sign #1: Your sites go up and down like a yoyo.
This one is a no-brainer. If your website is inaccessible at random times and your uptime monitor frequently emails you downtime notices, then it’s probably time to transfer to another host. Who knows how much sales you’re missing because your host can’t even do their primary job?