123. A lawyer must not, directly or indirectly, pay or offer to pay compensation to a witness or offer the witness any other benefit which is conditional upon the content of his testimony or the outcome of the matter.
However, a lawyer may agree to pay:
(1) reasonable expenses incurred by a witness to appear or testify;
(2) reasonable compensation to a witness for loss of time in appearing or testifying; or
(3) reasonable fees for the professional services of an expert witness.