Two of my first deals under contract I had made the rookie mistake of putting the property out on Craigslist with the address. I had lots of people I didn't know apparently visiting the houses, knocking on the doors, and telling the tenants the houses were for sale (the tenants were unaware ) and they wanted to talk about buying it! Even though I specifically stated the houses have tenants in them and not to disturb them.
Anyway--- rookie mistake--- and the seller heard about it and called me up and was furious and said the deals were off the table and he had sold one house already (what?!?). I explained that I am an investor and I am in the business of making a profit, whether that's fix/flipping, fix/renting, or simply selling the house to someone else. According to our agreement I could market the property, and I was doing that to establish market pricing so that we could figure out the best way forward.
I was very respectful and friendly, in spite of the situation, and the seller eventually calmed down and I salvaged the relationship and respect between us. I even negotiated the deals down further over time!
Ultimately, these deals didn't close due to my being too conservative on them, but it showed me how important it is to stay respectful and friendly, even when it seems like the sellers are trying to back out and screw me :)