the owners of the coins will complain, they will do so on forums where they can do so anonymously and the credibility/trust of the mixer is called into question

the owners of the coins will complain, they will do so on forums where they can do so anonymously and the credibility/trust of the mixer is called into question. (These tend to be forums where the users are in need of bitcoin mixing services e.g darknet markets or hackign forums) These mixing operations work on trust, as long as they are trusted people will use them, one too many stories about missing coins and it will be seen as a scam and avoided.