There are 4 things that can check yourself, whether your level of sincerity is at what level
1. The level of forgiveness when Someone really makes you angry
2. The level of giving, when Someone comes for contribution
3. The level of ibadah, when No one is watching you
4. The level of speaking the truth, knowing that telling the truth will land you in trouble..
If we really do things for the sake of Allah, then the above things are really easy to do, as you have this believe that Allah is the ONE that is ALL Mighty, and that fellow human beings are merely people with such limited power..
Just audit yourself....