I propose the forum to do the following, pay $5 per day to ten forum members reporting more than 1000 good reports per month. pick ten people and pay them a total $1,500 to have them reporting 10,000 good reports.
this will increase the race of reporting. It may also increase the spamming more and more. Spammer will make alternative/duplicate account for doing spam and report those from their other account for earning.
If you want to give some type of benefits ,then provide them some type bandage/sign(that is going on) in their profile according to the reporting and accuracy.