I buy iphone 7 from someone but the guy remove her account from the phone so I decided to create another account to sign in keeps saying verification failed can't sign in another account....

It is probably not removed from your device yet.

If you are the owner or the owner has shared all information with you then open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the owner and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password with you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their apple ID.

Did you set this phone up from the Hello screen with your own Apple ID?

If not then is is activation locked to the original owner and will become useless to you very soon.

You need to contact the previous owner and ask them to do this:-

Before you sell your phone...

https://support.apple.com/en-us/HT201351