These type of scammers look for non-tech-savy people. Software like Teamviewer detects "likely" scammer activities and warns people about scams if you get connected, for example, to an IP geofenced from say India and you are not in it:
We have taken the necessary steps to make sure that the remote IDs can no longer be used for illegal purposes and we are constantly working on new methods of finding and blocking such users. TeamViewer will display a warning message if an incoming connection with a potential fraudulent background is detected to warn our users of the risk of a potential scam
To avoid these kind of detects and warnings the scammer sometimes let the client initiate the connection bidirectionally and then take over - if you are fast you can bug the scammers PC with something that allows you access before that happens.
Sometimes scam baiters leave e.g. a "creditinfo.xls" in a folder "FinanceData" on their desktop in hope that the scammers download it and open it. It contains a macrovirus bugging the scammer's pc and allowing remote access (not by the same tool, but providing their own backdoor).
Both things are probably borderline illegal.
There exists other ways as well - Jim Browning for example sometimes shows that he leverages WireShark to trace network connections and traffic back to the attackers. If/what he uses exactly to bug the network he intrudes into is probably not shown by a reason - I think he's cool none the less. The tool he uses does not use teamviewer, but other ways of backdooring the networks of the scammers.