The title of this question is a little misleading, for the question I thought you were asking:

Do unframed prints sell better than framed in person?

ie in a showroom I feel the answer is undoubtably framed photos sell better. They look better, they stand out more and feel like you care about the image more.

But it sounds like the question you're asking is:

Do unframed photos sell better than framed in my online store?

Is a totally different question and has a different answer (from me as a consumer) which is that its not as cut-and-dry in that 'it depends' and there are many instances where I would be turned off if I had to buy the frame.

The difference is in a showroom, the frame does a lot of magical stuff for you like I mentioned above, it sets it apart from the wall, the person can see how much care you put into framing (which is an art itself) which reflects on you as an artist, and when purchased they can take it home and hang it. When its online none of that magic comes across, shipping is MUCH more expensive because its fragile and while they can admire the photo online its harder to get a feeling for the framing job.

As long as you don't discount your unframed photos (in the sense that the framed photos are only marked up for the framing job) this shouldn't impact your net profit at all.