I remember an expression that's something like 'you're just giving me words.' The idea is that someone says, 'yeah, i'll do abc.' And you respond... 'Okay, let me know when it's done, so I can check.' And they respond. 'What? You don't believe I'll do it?' And i want to respond, 'I just want to make sure you're not 'expression goes here.'
Paying lip service
From dictionary.com Lip service:
insincere expression of friendship, admiration, support, etc.; service by words only:
He paid only lip service to the dictator.
In your example, the response would be "I just want to be sure you're not simply paying me lip service". That is, you want to make sure that the statements of agreement are backed up with suitable actions.