I really cant understand why you would ever sell YOUR credentials
I really cant understand it at all. If it's a competitor wanting info, then surely you just sell them the info?! Preferably Info that you already have, and dont have to go digging for (potentially leaving a trail). You giving them access, so that they can go searching, is going to be bloody obvious in the logs, as they stumble around various systems they are not familiar with (OK yes that probably looks like standard C-Suite bumbling as well, but the things the Competitor wants are unlikely to match the standard C-suite bumble - which is to see and understand as little as possible!).
Once the login is rumbled, you'll have to come up with some excuse - must have been hacked, etc. - but that's it down and dusted, your accounts are now being watched closely, and so it's not likely you can sell them again... You got a one time pay-off, woopty-doo.
If your selling to the sort of access brokers that will then be selling your data to the malware scum, well do you really think they are not going to be scraping all YOUR data at the same time? And posting it for all the other Malware Scum to make use of. Bank Accounts, addresses, etc. All that is available from HR and will be taken. I'm sure the nice Malware Scum will remove your details frm the list. I'm sure they will.. *wink wink* That seems like a great way to make yourself a prime target for future scams, since your clearly a few sandwiches short of a picnic, and they have the wonderful blackmail material that you have already sold the credentials once, so guess whose going to be asked for them again AND again AND again... Maybe they'll throw you a few coins for your troubles. But I wouldnt bet on it...
I really cannot understand why anyone would sell their credentials - I guess 1 in 8 people being a few sheep short in the top paddock, sounds about right. Probably the figure would be higher, if more people knew willing buyers...