I'm absolutely confident they are banning manually, the question is: what are the criterias? My english isn't a native language , but I hope you'll get the point .
1 ) All your bots have same Ip same mac adress = Means 1 comp and you have static ip - Pretty risky - that would be nice if somebody told us they never been banned using such a way of botting.
2) All bots have same ip but different mac = VM or just different Comps , it's pretty safe but Ip is the same so probably we need detailed information to prove if somebody was banned choosing this option
3) Dynamic Ip + Vm = Basically it should be the most safiest way of botting , Would appreciate links to smbdy got banned using this method . But if u use a lot of bots - probably they can do the next thing
4) Blizzard has an automatic RMh with(I suppose) the statistics like who sell , and how much per account - (same goes to the buyers -but forget about them). Probably they have criteria if they have some doubts they manually check the amount of sold in $ euros and other currencies . If it is higher then XXXX amount ( Doubt they manually check where do the items come from i mean they wont check the trades in game) and your Ip or mac look suspicious they do ban just all the same vm/ip account (I presume they even could check for an instance the online time of suspected accounts, and do it manually) So if u have the Vm And Dynamic ip some of your bots could survive .
Afterall, I'd appreciate the links to different bans or the commentaries of the people whose accounts were banned. As for me I use 2 accounts to diversificate the money I make - dynamic ip and 2 different computers - botting strong never get banned since sarkoth noob stylish fails ( lost 3).