A good indicator of the overall condition of the hair and its ability to withstand a relaxer service is:

Perform a preliminary strand test

Explanation:

Subject to the application of hair treatment or intended alteration of hair color or properties, a preliminary hair strand test may be performed in other to examine and establish if the hair in question is suitable for the process. The preliminary strand test will give insight and idea about the possible result of the intended process, and the stylist will be able to infer if the hair is suitable to undergo such process or not. Hair stragd test may be necessary prior to relaxer application, hair color change and so on.