Poor coverage

I am having network problem in my bedroom. If i want to use wifi i have to move to my dining room, same house now i am buying extra data for to use my phone. And recently i am thinking of buying smart tv in my bedroom so i cannot affort to buy more data while paying for wifi. They told you they have to install access point which come with extra cost. My question was how did their technician asses the coverage on my house before installing the wifi because i dont understand. I did not get respond