Bill Gates did this stuff dealing with IBM et al.

If you CAN do X, and the only thing stopping you from getting the deal is the other side's perception of you, then influencing their perception (i.e. lying) can save the deal, save your company, and solve their problem -- all at the same time.

It can OFTEN be in BOTH your AND your client's best interest to lie.

And ask for forgiveness later after they are happy with you, IF it ever comes up...