Just Because the client has been with you for a very long time does not make them a great customer to do business with in today's market.  Ask yourself WHY they are a long time client.  Is it simply because they can't get the same level of service for the price anywhere else?  Is it because they are your friends?  Why do you feel that you need to keep giving service to this client?  That client prevents you from investing time and material into a profitable job.   Would this client support you if you were down and on the verge of closing your business?   Are they on a fixed income?  We certainly aren't! I need to cover my expenses:  wages, fuel, rent, taxes,etc.  

As business owners and managers, it is our position to insure that our company is healthy and making a profit.  We are in business to make a living for ourselves and our employees. If this client is a charity case and you can use them as a "good will gesture", and the gesture is  acknowledged by others, go ahead and reap the benefits. Otherwise, it makes no sense to keep doing the service and not making money.  Spend your time investing in new, profitable clients.