This one could cost you hundreds, thousands and maybe more depending on the work you need to get done. Do you due diligent and compare quotes and interview the prospective contractors before committing to a contract. There are a few things you have to ensure, that the contractor has insurance and is liable for the work they do for you. Some possible red flags will be mom and pop contractor who uses their home address as business address. Always ensure you check that there is a real address and contact number should the contract go wrong. Police report requires contact information and without it you are as good as nothing.
Communication is key and if you sense something is wrong, document document and document. You will not remember the details a month down the road. Gather all your information while it is still fresh in your mind. The one thing most scammers have in common is they try to relate to you. They will make up stories just to have a common trait with you so you let down your guard. Once you let down your guard, you might oversee the red flags. One thing you have to remember is scammers are out there to get you and you have to outsmart them to not get scammed.