Reasons to include a frame in the price of the wall portrait:
1. It gives more control of how the photography leaves your studio.
2. From a customer service perspective, the client is able to make all of their decisions when they place their order and they end up having a finished product in a few weeks that is READY to be displayed.

Many photographers who do not include a frame in the price still present the print to their clients at delivery in a suggested frame that is then available for purchase at a discounted rate.

Reasons:
1. Makes the print look much nicer.
2. Easy for client to just pick it and not have to make another stop at a frame shop.

You need not stock nor should you many different styles. A couple of basics will do nicely. Place the print in the frame, make the presentation. Your client gets the idea of how nice the print will display when placed inside what ever frame the finally choose. At the moment they can take an easy step and accept your frame or you can remove it and they can make another stop at a frame shop. Either way they are happy, you offered a convenient service that is appreciated.