Dishwasher - oil and water inside

Hoping someone can shed some light. Rented a house for a weekend getaway. Decided to to use dishwasher and hand washed. Owner had someone look at dishwasher 2 days before our arrival for minor problem, which we were unaware of. Two days after returning ho e from angreat weekend owner accused us of putting oil in the dishwasher and it sitting in the dishwasher with the water and now we are being asked to pay for a new dishwasher. Is there anyway ghat the sink water could back up to dishwasher or any othe ecllsnation. Desperate for advice! It is also septic tanks.

Don't know much about appliances , but if it's not draining either the drain hose is clogged or the pump has failed. Have him send a picture of the plumbing under the cabinet

Good idea. Have him send pictures of how the drain is connected to sink and pictures of the damage.
We can at least confirm if it's connected properly.
include the state you're in for code compliance.

WHO ? looked at the dishwasher 2 days prior to you moving in ?

I would be looking for that tech, to find out WHY he had to service the dishwasher.

You MIGHT be being scammed...tech could have told owner he needs a new washer, then owner he blames you.