The price you paid is VERY fair .... if everything works. I wouln'nt worry about the missing items, because you got more than your money's worth - HOWEVER, I would ask that the seller reimburse you for a trip to the shop to "clean & service" the mixer. I'm not sure(shure?) about that missing mic model, but with all you got ..... it's stilla deal. I'd be happy if the seller took care of the repair, and maybe threw in that missing speaker cable too.
Don't split hairs about the mic unless it's really important to you. The 6 SM58's are worth almost $500 by them selves. You got a great deal .... if it works.