When playing CS: GO, every player has a hidden Trustfactor that is only visible to teammates in a party if they have a Trustfactor that a lot higher than yours.
The specific factors on how Trustfactor is calculated aren't public, but there are generally some things to do to increase it.
Just by playing the game regularly and preferably being friendly while communicating with the team, you will increase your trust factor.
Aside from just playing the game, you can also enhance it trough a good looking Steam profile (other games with some playtime, Steam Level), Commends left by players in-game, or a Prime status upgrade.
You can also increase it by adding a phone number to your Steam account and enabling the Steam Guard.
Your Trustfactor can obviously also get lower if you get reported often, and you are a bad member of the Steam community (kicking people, being unfriendly, etc.)