In a business you are going to have a range of clients that you work with, projects will differ. Some clients you will be able to use as an example of the work that your business does, while others may be more of a one off which does not show your best qualities.
Using client’s as example’s, testimonials, or case studies, can and does work for many businesses, but the often fact of the matter is that they do not always last. If you do a great job for a client on a marketing campaign, it has a limited life that you can use that as an example. Maybe a year later when the campaign is over the company decides to go with another business to do their next campaign. This may be no direct reflection on how good your last campaign was, but it will give people perceived ideas that could see using this campaign as an example not such a good idea once it is no longer being used.
While if you are using examples or testimonials in any respect it needs to include a spread of clients or projects. There is a way to highlight work that will never go out of fashion. This is to create projects of your own which highlight your work. Of course this works best for particular types of products, it is something you should consider.
Maybe it wont work if your specific type of business is building large commercial developments, as you may not have the finance to invest in your own projects. However if your business is something like Web development, you can for little money and quite easily set up a range of project’s that are your own which can show off skills that you have, and be able to offer these as examples for your own business.
Of course what i am suggesting is not that you deceive your clients, be open with them and say these are my own projects, but they do show many great features of the work that i can offer you. Being honest, and showing a client that the work you do is good enough for you, will often give you a little edge over your competition, who may just look to show off their best projects.