I've recently enlisted some help on this too.  The person who is doing this is someone who I totally trust.  We agreed on comission only plus I give him some money to cover his petrol (+ a little bit).  The commission we agreed on was 50% of what I take for the first clean plus 50% of what I take for the second clean (if anything).  Assuming I get 1 job per 100 leaflets, this should be about right.  If I get a lower response than that, it would still be OK if the jobs are decent sizes.