definition of a probative offer?!?

[arkybarky]

Can anyone tell me in layman terms what a probative offer in accordance with Scottish Legal Practice is??
I'm looking at putting in an offer leasing premises and have been asked for one of these, do i just need to have it counter signed by a witness? can this be anyone?
Your help is greatly appreciated in this matter.

 

[Billmccallum]

Having the effect of proof, tending to prove, or actually proving