How can these customers become happy? You can throw a cable testing tool or two on top of the new switch, but then you have added hundreds or thousands of dollars to their bill and added hours of time required to test each cabling run. Your customer probably still won't be happy.
Sometimes, even in this climate, spending more leads to more happiness. I recently visited the Adtran folks in Alabama, and one of their boasting points is a line of Gigabit Ethernet switches with built in cable diagnostics and reporting. They have several models, but the model number for the one I'm thinking of now is the NetVanta 1534.
Not only does the NetVanta 1534 support wireline speeds for all connections in and out, it includes a cable diagnostics mode that identifies problem cables, tells you if the line is open or shorted and lists the distance away from the switch where the problem is. That will make your customer happier than a cheap switch and some testing tools, because it will indicate problem links so they don't have to test all their cable runs.
Being a big fan of the 80/20 rule, I regularly see that users barely scratch 20 percent of the capabilities of many of their technology tools. You may make your customer happier, and save them money, by training users how to better use the tools they have rather than trying to upgrade them. This really saves money when we're talking about internal support teams, since you don't have to pay for training hours and the money you don't spend on the upgrade is your own.
In tennis, successful players aim away from the lines and more toward the center of the court when under pressure. The same applies today. You don't have to get creative and outthink your customer to make them happy. You just need to provide technology that hits squarely in the center of your customer's sweet spot and not push boundaries. If you're internal, this provides a near term (cliché alert) win/win for the tech department and the user.
If you're an outside service or sales support person, the same thinking applies, but you must think longer term. Teaching and training customers to better leverage existing tools looks like a winner for them but a loser for you. Actually, making your customer happy always yields better results than selling your customer a particular piece of hardware or software. Happier customers are long time customers.