Yes, you certainly can. Framed and ready to hang works are preferred by collectors as it reduces work and effort for them.
We know that framing is expensive and you wouldn't want to frame all your works prior to sale. If you can source pictures and prices of frames, you can display the artwork as framed. Once it's sold, you can get it framed.
We understand that it might take a few additional days to have it framed. Just mention this extra time (keep 1-2 days as margin) in your artwork's description so the collectors' expectations are managed as well.
It's important to note, that while Bluethumb insures your artworks for damages in transit, Bluethumb does not insure the value of the frame or glass for damages in transit. You'll have to make sure your artwork and frame are sufficiently packaged and take out any insurance for frames/glass yourself.