Sounds like you might need to put a little more effort into your hiring process in order to increase your chances of hiring employees who will be a good fit for your company.
You are the one who makes the decision to hire. Don't make the decision to hire until you have acquired a reasonable assurance that the candidate sitting in front of you is the right person for the position you have available.
Get a few books on hiring employees/conducting interviews/managing your employees.
Here is a list of books I recommend:
How To Become A Skillful Interviewer by Randi Toler Sachs
How To Hire The Right Person by Denis L. Cauvier
Hire Your First Employee by Rhonda Abrams
The Manager's Book of Questions - "751 Great Interview Questions For Hiring The Best Person" by John Kador
The One Minute Manager (this is a series of books) by Kenneth Blanchard and Spencer Johnson
Everyone's A Coach by Don Shula and Ken Blanchard
Managing For Results by Peter Drucker
Management Basics by John & Shirley Payne
13 Fatal Errors Managers Make And How To Avoid Them by W. Steven Brown
Leadership Secretes From The Executive Office by George Hathaway
The E-Myth by Michael E. Gerber
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