How to tell if a pair iem is good?

Hi, i got my second pair of iems truthear gate, i wanted to try a different pair of iem just to see a different sound signature and was looking for something on the cheaper side. My first pair of iems were the zero blue(1) been using those for the past 10+ months and I got really used to them.

Is it normal that listening to another pair of iem sounds a lot worse? Something like being too used to the same old pair of iem.

For some reason when i listen to the truthear gate everything sounds muddy, has little to no bass, vocals are bad and weak... Can't really find a reason to listen with them since everything sounds so bad. I did try 2 different ear tips, one that his small and another that fits well my ears, i do hear a small difference but i think using a better tip just made me realise that they are still pretty bad.

For people with lots of pairs of iems how do you go from using one to another? Since I assume some sounds way worse then others.