My parents bought a place that only dogs had lived in for 3+ months. Had the run of the place – sh*t everywhere. It was awful. I’ve no idea how they saw past it, but they did and more than doubled their money. Anyway, before we moved in Rentakill (I am pretty sure it was them, but it was 24 years ago!!) deep cleaned it twice, once before and once after the carpets came out. Honestly no problems with smell in the 7 years we lived there.
The place we bought 3 years ago has solar. Ours are owned outright and we got asked a number of Qs but it was ok. I did certainly get the impression that if they are rental ones, it does cause more issues, potentially (depending on the lender) requiring them to be removed prior to the sale completing.