If you adopt a para-legal stance on warranty, that is to say if you give a warranty and a client/purchaser accepts it, if something goes wrong, you will be answerable for repatriation.
In traditional photographic prints, you must be absolutely certain from the start you can guarantee the quality and perpetual wellbeing of the print. This is very difficult to do if you sell just raw prints, rather than matted and/or framed. The latter two options discourage the possibility of the print coming to harm in unskilled hands e.g. the purchaser likes you work but no doubt may have little idea what constitutes proper handling until it is framed.
To my knowledge over the years, only Ilfochrome prints have been warranted by photographers (here in Australia) because the process is proven in terms of quality and stability, and selling of raw prints is generally not the norm (for the reasons outlined above), more commonly framed ready to hang.
I am not convinced that B&W traditional darkroom prints can be warranted on whatever premise, nor for that matter can archivally stable (over whatever time) giclée prints. Both products are subject to adverse reaction in unfavourable storage and handling.
You might wish to give very serious and deep thought to any warranty offered and your capacity to redress any difficulties that arise. It can potentially put you in the legal hot-seat.