1. Do not share items or account information with another person you know online.
2. Be careful that there can be a character with a similiar name of your friend, or guildmate trying to borrow item from you. Confirming the person's identity via messenger, phone etc are good solutions.
3. Be careful with the files you open (recent downloads). Also I'd recommend checking every downloaded file with an anti-virus. Dont click the link if you dont know if its safe. I played wow before.ebay is the best choice for the gold =). Silkroad and kinght online. I choose Gkplayer for gold. selling gold like 4 years.
4. Please be careful to verify alphabets when transferring items with a character that use I and l in its name. w and vv. NI and M. cobra_ and cobra. lots of similar name.
5. Do not trust a person who offers you first to pay money and give item for upgrading it. Most of cases that a person approaching to you saying he/she will upgrade your item are fraud. The person will only take your items and money, and won't return the item back to you.