1) Don't just trust the status of a member, anyone can be a hero member. This just means that he invested some time on his membership. He can always decide that a profitable scam will be a good payment for his time. However, a Hero account without negative feedback can be sold for more than 0.5 btcs. Therefore, he probably won't scam you for less than that, because a negative feedback from you would lower its value substantially.
2) Never deal with anyone without doing a search in the forum with his nickname, in order to check if he has scam accusations.
3) Ask for his coin address and always search it on
http://blockchain.info,
www.cryptocoinexplorer.com or other similar site, to verify if his address has the amounts he wants to sell.
4) Be very suspicious about proposals well under market price or if he accepts your proposal under market price with no negotiation.
5) Look for the reputation/trust of the member, checking also his successful trades, in the form of vouches from the other party on the deal. Be aware that positive trust can be forged by making and using more bitcointalk accounts and the trust system can be more or less avoided by changing its settings.
6) Even if he has some reputation, never send all the money in one transfer: send one first small tranche (ex. 0.05 btc) and wait for his payment. Send a second little higher tranche and wait again, etc. Small increments, because he might decide to pay you the first and second, to scam a bigger tranche. Always suspect if he doesn't accept to trade in small tranches, unless he has an excellent reputation.
7) If he has no reputation (specially if he is a newbie or Jr.), even small tranches are very risky. Better use an escrow system, like the one of
www.btcrow.com, or a trusted member, or you might need to send more than 10 very small tranches. Think well before sending more than 0.15 btcs (it's considerable money in some countries) and only after 3 or 4 successful payments of 0.05 and 0.1 btcs.
8] For big amounts use an escrow system, unless the member has an excellent reputation. If he doesn't accept, forget the deal. Always protect your capital.
9) Only trade codes (ex. of virtual gift cards) with members with a very good reputation or using a very trusted escrow member that will have to go to the account and apply the code himself. The buyer will have to give the escrow person his password and change it again after. With an automatic escrow system, the buyer can claim falsely that the code was already redeemed when he received it or that his account was blocked after.
10) Don't sell any cryptocoin to paypal or other reversible system, unless the buyer has good reputation. The buyer can chargeback and, since it's against paypal's TOS to trade currency, paypal usually gives your money back to the buyer.
Here is a list of escrow members:
https://bitcointalksearch.org/topic/escrow-list-108716 
