If you dont have a Rav, how would you handle the following situation.
As a favor, we allowed someone to stay in our apartment for a few days. This guest had a chezkas kashrus when he moved in. Upon the guest moving out (upon our return) , we discovered in the garbage empty boxes from treif pizza, and other treif (not a question of whether the hechsher was reliable) foodstuff. Guest only had access to a microwave oven. Melted cheese was found in the microwave (and treif pizza boxes were found in the trash) . Must we assume treif pizza was warmed in microwave despite the readily available kosher pizza in the neighborhood. If yes, must we assume it was also used for neveila (or chazer) despite no evidence of such food. If yes, may we kasher the microwave, and how. Furthermore, this person stayed by someone in the neighborhood for a few days prior to staying by us. Must we alert the neighbors that their kitchen and utensils may be problematic. May we (without any proof, we only have the circumstantial evidence of the empty boxes which is certainly compelling evidence – but how does halacha see it)? Perhaps the person has a chezkas kashrus until there is a reason to assume otherwise? Is our “evidence” enough of a reason?