On this bug report on Github https://github.com/googlesamples/android-play-billing/issues/2#issuecomment-305380836 we were asked to raise the issue here.
The issue is simple. The user has 2 or more accounts on their phone, let's say xyz@gmail.com and abc@gmail.com. They install an app with the account xyz@gmail.com. They purchase some IAP items. The app updates and now the app is under abc@gmail.com and the user has lost the purchase. This happens a lot when using staged rollouts.
The main issue, as developers we aren't allowed to let the user choose which account to buy with or which account to check for purchases with.
The second issue, the Play Store app on Android ignores the user account selected on the hamburger menu. The only workaround for this is to use the Play Store website as described in this workaround https://github.com/googlesamples/android-play-billing/issues/2#issuecomment-259108286 on the same bug report.
I don't know what the ideal solution is, all I know is that this is a huge hassle for developers leading to a lot of 1-star reviews after each update.
EDIT: As pointed out in a comment, when I refer to multiple accounts I am talking about multiple Google accounts for a single Android User, I am not talking about multiple Android users within the same phone.