A lot of times my clients did not have IT staff and were not running any sort of password managers so it was interesting. So two things I had them do routinely

A lot of times my clients did not have IT staff and were not running any sort of password managers so it was interesting. So two things I had them do routinely are below, though some would still just send me an email with username/password in it (always felt dirty). Best overall option, have them create a user account for you with a temporary password on whatever service you need access to. That is safe to send via email then you immediately change it. Then when you are done with their project they can just remove you. If it is for a service that they can't create more user accounts, I would have them email me the user name, and either tell me the password over a phone call (choice 1), or text me the password on my cell phone. While still not the most ideal, it would minimize some of the exposure of just having a username/password in a single email. I also advised all clients to change the username and password often and especially when I was complete with the project. I told them they should do that in reference to any company or freelancer they use. All this for the 95% chance that you will still receive passwords like "password1", or their company name with some date appended etc. Point being any middle schooler could probably guess the password. I'd usually always send an email about password security in these cases as a helpful service but also a little bit of a CYA in case anything ever happened. So I could point to them that I warned them to change weak passwords.