Most of these problem members, scammers and sponges fit a certain profile. Several of these items apply to them:
1. "long time member" but has years of public inactivity
2. Contributes nothing to the site socially
3. No ties to here, hence no reputation to worry about
4. Has made questionable decision on hardware and sales
5. Only lurks in the market
6. First to post in giveaway, free stuff threads or raffles
7. Buys/sells things frequently, mostly at profit (flipper)
8. Active for a short time, then only posts in the market
9. Insulting or dismissive of the forum regulars when questioned about rules, prices or expectations of sellers
10. Demands +4% or Paypal gift on transactions with little reputation to stand on
11. Buys at "community prices", sells at "ebay prices"
12. Runs multiple accounts to hide market activity