As I am new in your market I’m searching for an competitive edge .Obviously my preferred way to do business in with an assignment of contract, but as I’m new and you cannot vouch yet for my professionalism or reliability I want to setup a construction where the seller can call the title company to be assured that the deal will go true.My question :Is it possible to put x amount for example 200 000 $ on an escrow account at the title company which will serve as a guarantee for the seller?

Active - connect with brokers in your target market, find a reliable property management company, connect with banks for financing. 

Find a good property manager: If you are planning on adding out of state rental property to your investment portfolio, you should know that managing a rental property out of state is a completely different ballgame than managing one that you can make regular visits to, and you absolutely must work with a reliable property management company.

The biggest problem is getting reliable crews.

Agreed with @Jay HinrichsLots of red flags and no google reviews upon googling...Plenty of reliable and reputable lenders out there on this site as well as a google search away

Can someone suggest me a reliable source of information where to get the historical evolution of house prices in Florida; specifically Broward County (Single Family)?

Not all will continuously change terms along the way or ask for extra docs at the end, important to judge the lender's reliability and process as much (if not more!)

We have a potential tenant who is very interested in the unit as her mother lives in the same complex and we received a very positive review from her supervisor who not only stated that she has been a reliable employee but is expected to stay with the company for a long time.

Spread out into a few different markets for your short term rentals, and acquire some long term rentals or commercial deals for more steady, reliable cash flow.

Since I would need a good idea of what my upfit cost would be before I offer on the building, I was wondering how much do I need to do to get an reliable estimate.