Pet or future breeder I'd have two major issues with this purchase.
One is long term damage to the snake from this exposure and in fact was it this exposure or was the snake fully healthy in the first place. I'd want to know where this snake came from and speak with that person.
The other would be trusting the person I'm buying this snake from. There is something very wrong with a snake going into QT in an enclosure that was never disinfected from the previous snake. That shows a serious lack of basic husbandry skills. Also I really question what was sprayed in that enclosure. For it to be deadly still after all that time, well either something is not being said truthfully to you or the product used was never reptile safe in the first place.