Commercial tenant - transitioning manager

[Christopher Lewine]

Hello! Last year in my first RE deal I bought a small multi-unit mixed residential/commercial building. the ground floor has been occupied by an antiques store for the past 18 years. Multiple dealers pay rent to the store owner, who pays rent to me. The store owner is retiring and wants to hand off management of the store to one of the other dealers. 

What kind of screening should I do as a part of this transition? How much information would you recommend that I gather on the store and/or the new manager/owner before signing a new lease?