If I have a buyer for my deli and my lease is transferable, can the landlord stop the sell even if the buyer is a creditable and has knowledge of the business?

Normally the sell will be based on the lease transfer being approved.
If there is a reason legally not to allow transfer, yes he can stop it.

Why does the landlord not want to allow transfer

Because she say"s they lack experience in the deli business. The interested parties have a café and want to upgrade to food. I offered an unlimited time of traing if necessary. Landlord is still not pleased.