Your best bet when working with a seller who has multiple properties is to avoid the temptation to try and buy the entire portfolio upfront. You're much better off asking the seller which of the properties is the worst one. "Which one is in the worst shape, is in the worst area, is the hardest to manage."

This gives you a chance to prove yourself as capable of handling problems as well as maybe even getting the seller to provide creative financing since the property may not be in great shape. Once you've done this on one property, you've created a track record and hopefully also created some rapport with the seller which can more easily lead to acquiring either more properties or the entire portfolio.

This method has a higher chance of success than trying to get the entire portfolio up front.