"You are selling his cat?"
Translation:Sprzedajesz jego kota?
if it is a question i would suggest the proper translation is - are you selling his cat? rather than - you are selling his cat?
For me, it is rather a statement than a question, but OK I conceed the point ;) but it's purely contextual :)
No. Perfective words do not have present meaning. They only have past and future tense.
Sprzedasz means You will have sold.
Most verbs in Polish have only one version of present- imperfective verb.
Polish perfective verbs inform us that the action is or will be finished. Polish imperfective verbs infom us that the action takes/took place/will take place.