The short answer is only you can tell. However, there is a lot that you, as a parent, can do to help your teen earn your trust. The first step is to understand that trust is built and based on behaviors. So to the degree that you can give your teen clear instructions as to what's expected of him/her and the degree to which he/she can meet those expectations - - that will set the level of trust you can have with your teen.
The second step is to create realistic expectations of your teen's behavior. The expectations you might have of a 17 year old are quite different from the decisions and behaviors you can realistically expect a 13 year old to meet. You should also take into account your teen's specific maturity level. If your teen hasn't shown trustworthy behavior in the past or tends to be immature for his/her age, adjust your expectations for his/her behavior accordingly.
So first, identify the areas in which you believe your teens are ready for some freedom. Then set clear guidelines as to what you expect from them, whether it's meeting curfew, not driving after dark, or leaving the door open to their bedroom when friends are over. As your teen complies with the rules, that teen can then earn more trust and more freedom. When (be realistic here as well; breaking a rule is a "when," not an "if") your teen breaks a rule, make sure he/she understands the consequences. However, to keep the communication and bond strong, you needn't make your teen feel unworthy or immoral for having broken a rule. Simply implement the consequences, which may include dialing back some previously given freedoms; and let your teen know you have confidence in his/her ability to regain your trust.