So far I've rented out two characters.
First was a 62 mage to a2gold.
First time I did it was going ok, after I had given them the account details within the hour they had logged in and started farming. At the end of that day I logged into to wow.com to check if the password or details had been changed. Nope all info stayed as they had said. So I let them continue. Kept checking up on my character before i left for work and when i got home.
Into the third day I was grinding on my druid and noticed that the mage had gone off line and hadn't reappeared for a couples hours. These guys are online on the character 24/7 and only log off for a min to put items in the ah on a bank alt they create on the account.
So I try to login and got the message saying password was incorrect. Check my email and it said that my password had been reset. Tried to login with new password and get the message saying that I was banned. Got on the phone to blizzard and spoke to one of their support guys. Told them that I had been busy with work for a few days and just tried to login a few minutes before and received the banned message. He informed me that the account had raised red flags due to being online for more than 72 hours.
I start to play stupid and asked him how they got my password. Everything was sorted and the account was unbanned and had him reset my password once again with the excuse that if i was key logged they would have my new password because i tried to login.
So Round one,
Before Renting : 62 Mage with nothing on the account
After Renting : 66 Mage. Approx 750g a bank full of cloth. Bank alt on the account had mail which had been returned totaling just over 1500g.
Next account was a 63 priest.
This time I used wowpl.com as everyone was ranting about them on these forums and how wowpl were paying good gold.
I couldn't risk this priest account getting banned thou due to the account not having anymore restores left and having a few warnings for exploits.
So this time I gave out the details to wowpl. Took them a good day before they had even started. But like a2gold farmers, always farming the same spot and online 24/7 (Probably the exact same group of people). But this time, as the farming had approached approx 50 hours straight I logged in on an alt (separate account) did some ah farming and kept an eye on the location of the priest. I had also changed the password to the account via password reset(So it looks like account was keylogged). The second he had hearthed to shat I logged in.
Stayed off the account for a few days and no warnings to date.
So Round two,
Before Renting : 63 Priest with nothing on the account
After Renting : 66 Priest. Just over 600g, bag full of vendor trash and 16 primals scattered in bank, bags and auction house.
My Advice
Renting your account for a few days is worth it, just don't get greedy as they will be farming 24/7.
Make sure you keep nothing valuable on the account, trade it to a spare account or to a friends account a few days before you plan on renting it out.
Make sure your not in a guild and have little to no friends on the server.
Keep your quest log packed with quests in terrokar(level 62-65) or nagrand(level 65-70) as these are their usual farming spots.
If you are getting them to level your toon, make sure it is fully rested that way you get max amount of levels during the time they are farming.
Never let them farm on your character for more than 60 hours straight!
Before you give them your account change the password.
And before you take your account back use the password recovery tool to make it seem like they hacked your account.
Good luck and happy renting !