We moved recently into a new house. The real estate agents told us this house is brand new, was just built about a year ago, and have never been lived in or used. There was a stove in the kitchen which was apparently new (and it looked new) and there was a dishwasher as well. We used it. But afterwards I got nervous wondering if I could rely on what the goyim told me that the house is new. I mean, it is new but can I be sure nobody ever lived in it? I assume nobody did because there were no beds here and it was not furnished. But I just want to be sure there is no kashrus problem and halachically it is okay that I assumed it was all kosher? I already put many plates and spoons etc. into the dishwasher and many pans into the oven…
Under the circumstances, you may continue to use the oven and the dishwasher, and there is no problem with the pots and pans etc.
Although a non-Jew is not believed as a general rule with respect to questions of issur and heiter, there are instances where he is believed (see Shulchan Aruch, YD 83:7, and commentaries). The principle factors are whether or not the non-Jew testifies as part of his job — which he is afraid to lose — and whether or not his testimony can be corroborated. In the case of the question, there is an additional reason to be lenient, because the over and diswasher look new, and there is no reason to suspect they have been used — one can usually tell when an oven has been used. Additionally, the kashrus of ovens and dishwashers is a complex issue (which we will not enter into here), and it is possible that even if they were used, they remain entirely kosher. Putting all of the above together, there is no need for concern with regard to the oven and dishwasher.