The other thing about selling negs which one needs to be wary of is that folks actually print them.
Seriously, if they are printing your work - and it is not matched to whatever printer they are calibrated to, there may be serious problems.
I am not saying that I do not offer negs (actually, I do so as part and course), but I do worry that when I send my stuff to folks that it is being sent to everyone that they know...if it does not look good, I don't look good.
I prefer to sell small representations of the prints (no larger than 4x6) with the idea that all larger prints come through me.
James