We have a client who is wanting to provide a free and paid version of an app we are developing for them for the Apple AppStore. They are also looking at doing in-app purchases for upgrades. Is this something that can be done under our developer accounts. Ideally we would like to put it under our account and have the profits go directly to the clients bank account. Is this possible or does all the payments come to us and then have to be transferred to our client? Or are we best of getting the client to buy their own developer account?
No, that is not possible. Either your clients will need their own developer account you you will have to transfer the money to them every time apple pay out. As it is quite a mission to change you banking details, you cannot specify separate banking details per app
Unfortunately no, it isn't possible there are two case:
1) The app is released under your name. If you do this Apple sees you as the owner of the app and won't deal with or make payments to your client.
2) The app is released under the client's name. If you do this Apple sees the client as the owner of the app.
I imagine that most clients would want to release from their own account as they'll then "own the brand", since they'll be listed as the developer.