Of course, as you know the answerer just can't tell you the bare meaning for these kind of modals; so, my approach to answer would be setting the meaning of the sentence straight.
The salesman would have sold his products but he was late for the appointment.
Mr.X is a salesman. He was probably unsuccessful in selling his products until, Y offers a great deal of money for his products. Unfortunately, since he has a significant appointment with, I don't know, maybe his dentist; Mr.X has to reluctantly decline the offer. This is what one can fathom of the meaning of the sentence. Now, let's try to get these meaning from the sentence.
First, let's think "the second condition (his setting of appointment) was untrue". The rest of the story would be "the salesman definitely makes the deal and sells his products." (this sentence is stage 1) To state these two sentences combined (the ones in quotations) together gives us this:
{If the setting of the appointment was untrue, Mr.X certainly made the deal.}(stage 2)
The conditional sentence above, is the opposite of what the main sentence tells us. So, to make it apply what we need, we use "would have" + p.p. of sell to say that something didn't let selling happen, but if it wasn't for that thing, the selling definitely happened. This is simply step-to-step addition of meaning.
{Unfortunately, Mr.X has an appointment. He definitely wants to sell his products, but now he can't.} (stage 3) Which turns into "He/would have sold/but/has/appointment". Finally the main statement takes its figure.
And as a replacement, I think because it's almost about "definite" talk in here, and the probability isn't mentioned, there are hardly any 'three identical words' which would completely 'fit' in the sentence instead of these three. If one asked me to write a statement with the same meaning, I would prefer doing a recast.