(B2B) Sales person, how few prospects do you expect to turn into sales ?

Without giving details, My job involves adding a new function to an existing system, and we decided to find an off the shelf product rather than "make it by ourself".

This means that at the moment, I left the company basement, removed my lab coat and safety glasses and wear a nice shirt to go on the floor with nice windows (and weird hyper social persons) to talk with our purchasing department and meet suppliers.

I somehow feel bad to keep talking with B and C while knowing that they're proposal/pricing isn't as good as the one from A but that until purchasing closed the deal with A we cannot just tell them no. So how frustrating is it for you sales persons

At least when I break stuff in the lab it doesn't make humans unhappy

EDIT : forgot language flag