Hi Pankaj,
The Sinarback 23 is not expensive to buy, if you can find one that is. Your friend may have got a bargain depending on what accessories were included. The only accessories that I could offer would be a Sinar P2 Rotating Adaptor Plate, and FibreOptic cable with power supply. However, I am thinking it may be more useful for me to hang on to, rather than to sell for its current value. Whereas most clients these days demand a far higher resolution than what the 23 offers, it is more than adequate for ecommerce work.
Hope you have success finding the right digital back for your needs.
All the very best
Al