AhsanaAllaahu 'alyakum, regarding transactions. Is it correct to say that it is impermissible for one to jokingly sell or transact an item/service? Does this not fall under the category of lying

Deception is not allowed, of course, but sometimes jokes come out and it is understood, provided the joke itself doesn't contain anything forbidden. I am afraid you are falling into a trap, because there are many jokes you can say that do not include lying. When the Messenger told Abu Hurayrah (the father of the little kitten) that, it was not a lie; he was joking with him. So, let’s not fall into extremes.