hello friends i created an app and i want to sell my app to multiple clients.
i know that i have to change package name for every client but i want to know that can i sing that same app with same key-store for multiple clients with different package name.
or should i sign app with different key-store for every client
if is there no issue with play store.
Technically you can. There's nothing stopping that, and if you have a fleet of apps you generally do sign with a single key.
If you're releasing the same app to multiple clients as a whitelabel- Google has changed their policies on that several times. The last time I whitelabeled they used to say that the client should own the listing and have their own key and that you should just be an administrator on their account. But that's a policy guideline and off topic here, you should look into the latest rules yourself.