Lucrative is defined as
adj. producing a great deal of profit.
In the context, the speaker is negotiating with the listener and asking for the best possible price for something, which he intends to buy. Is it correct to ask for the "most lucrative offer"?
"Lucrative" is something that happens later, after the transaction. You could make a deal, which could then go on to be lucrative for you, but at the time of the deal, that is in the future and thus unknown.
Looking back, we could say "That deal turned out to be very lucrative", but at the time of the deal it's not appropriate as it hasn't happened yet.
Lucrative also has a connotation that the seller is making a mistake in selling it, or in making the deal: if it's going to be "lucrative" then that suggests they should hang on to it rather than sell it.
In the present tense, ie at the time of the deal itself, a better word to use would be "most attractive", or more simply "best".
