If you badly need a test series, you must buy from providers. Else following thing may happen
1.Issue from seller- The registered email ID can be used to reset password any time; (You can expect it any time as we are not registering with our email ID)
2.Issue from Provider- Chances are high to get locked due to multiple signin & changes in answers. Eg: if you joined a writing series, You will be easily pointed out with handwriting change.
Just 2 basic issues mentioned. So beware of re-sellers to keep your hard earned money safe.