I've seen this in the printing industry where I learned my trade. It's actually your job to educate the customer. They think they know what they want - they just don't know what it takes to make it work. This is where you use your experience to direct the customer to the product that will give them the results they desire. I know how I'd do the job properly for the expected results. But, of course, budget always gets in the way and we try to fit our best product into the little budget package - sometimes with less than expected results. I've done jobs as spec'd by customer, told them it will fail - did the job and had customer come back telling me I was right! Do the math, figure out how long they need it to last and make it with the best products you can.
cheers,
Dave
cheers,
Dave