You will not be able to verify this, so do not believe that they will provide complete anonymity. Still, I wonder why you want% 100 anonymity? I do not get the point of it.
The purpose of mixers is to completely obliterate any trails from past sources of funds to protect the user, so it is understandable that one user may request
full anonymity from mixing services although we know that it isn't really possible even on paper.
Bitcoin mixing sites, How to make sure that sites does not keep the logs, this is never guaranteed i understand [sites can store if wants]
No one can really be sure that sites never keep logs. If, however they have done the job and it is well done, I must say that that will be enough, but then again there are the paranoid ones that can't be satisfied even if the result is already laid bare in front of their eyes, and that we have no solution on.