I would say in my opinion buying a list is a terrible idea because there is no way to know if these business owners actually need your service.
You need to prospect yourself and grow a list yourself of people that NEED your help or services. This way you will know what needs to be done and how you can help, you can do research on the business, etc.
The key thing when prospecting and getting clients for any service sort of business is you need to speak the language of the business. Meaning if you are not knowledgeable in the industry the business is working in then they will not feel comfortable working with you, simple as that.
This is where specializing comes in. You need to specialize in one industry and learn everything there is to know about it. That way you will know pain points and struggles business owners face in the industry.
Just think if you were a business owner, let's say a dentist for instance and you needed marketing. And two marketers called you up, one does marketing for every industry and has basic knowledge of the industry. And the other specializes in dentistries specifically and uses terms only dentists know and brings up pain points you face all the time.
Which one would you hire? Probably the specialist.
It's all about researching the businesses and being knowledgeable in on industry. If you are knowledgeable in one industry you will find out problems and pain points.
Remember if you have a service based business your job is to help the business owner. Meaning YOU dont need them they NEED you. So ditch the list and become an expert in one industry.