Is this legal, a marketing company hiring people to serve debtors?

It is legal if you sign the paper, NEVER ANSWER THE DOOR, CHANGE YOUR MAILING ADDRESS and put every letter sent to you in the post box returned, if your mail man starts to get aggressive then he is haring you, unless your been served for serious offenses or proceedings like to be evicted NEVER SIGN ANYTHING, If you where in serious trouble the cops would of already been the only ones looking for you, the rest are illusion, ignore them.