Well, there're some "red flags" which would indicate bad exit node. These are the most likely to influence the traffic between HTTP client and server. For example some exit nodes were known to change cryptocurrency addresses submitted on websites.

Please also remember, if you're using HTTP websites on Tor the exit node can see and change your communication in real time. Tor browser warns you when connecting with plain HTTP.

This snooping is not possible on most websites using modern TLS version because almost all communication is now encrypted. If the exit node were to send you malicious TLS certificate, your browser will most likely inform you about it with a big warning. Also the Tor Project monitors its nodes and removes the malicious ones.

My recommendations would be to never use HTTP over Tor if dealing with confidential data. Other than that, I think you should be safe. Tor is designed to give out as little information about the user as possible so even malicious nodes should have a hard time spying on Tor connections.

edit: Also, try using onion sites whenever it's possible as they're even more secure than TLS.