You can give them the option of either not moving in or telling them to take it as is. Have you looked at the paint job? Is it sub par or are they being picky? If it truly is a bad paint job I would have the painters come back and fix it. If it looks ok to you have they told you what is wrong with the paint job? I do not believe you can make them not take the apt if they signed a lease but you certainly can offer them their money back and see if they take it. If they decide to stay these are the kind of tenants you need to be firm with in the beginning or they will run all over you.
Check paint and request "fix a job" from painters.It it is nice done-tell tenant to move as is or not.But...with tenant like this create check list,include appliance all doors windows,bathroom ETC.Ones they sign OKs they have to fix it on their own expenses(include this in the agreement).But...people like that -means trouble.