Does selling plates that I buy wholesale from a grape leaf vendor, and then retail them at his stand, make the money earned lawful or unlawful, and will my repentance be accepted if it is unlawful?

If the shop owner permits you, explicitly or by custom, to sell the dishes you bought from him in his shop, then your action is permissible. However, if he does not permit you, then you must repent to Allah by seeking forgiveness from the shop owner. If he is not satisfied, then pay him the rental fee for using his space for the past period. Buying dishes and selling them for more than the purchase price is permissible.