Yes you can say it (spelling is "customer").
To convince is to make sure in one's mind - I am convinced that is the man who robbed me!
Persuade is to give more plus reasons than negative ones, to make someone do something (I said it was the man who robbed me, but the $50,000.00 from the police made me say it).
Suitable is something which will suffice or is in the right place (a shirt for work)
It's not appropriate for me to ask for more money at work when I have only been there for one week haha
It would be inappropriate but it would be suitable to me, because I'd want the money :D
Is that ok?