A few thoughts on the diy hardscape business:
Notoriously POOR customer service from the hardscape manufacturers and distributors (layoffs, as you likely know) -opportunity to set yourself apart as a trusted souce that cares and follows-up.
Loads of low-quality pavers (won’t name names, but you know who they are) flooding the market. Scream about your quality and tell customer what to look for in a crappy paver from your competitors.
Customers need tons of handholding (proper paver installation/joint sand depth/sealing); isn’t rocket science, but it’s not easy.
Shipping is a major cost consideration. If you’re not already cutting deals directly with manufacturers in different regions to keep your pricing competitive you may want to approach them. Somewhere I have a spreadsheet of all the paver manufacturers across the US with contact info. I’ll hunt for it if you want it. This would go against your preference to cut the design to specs BUT if you can cut a deal with a manufacturer with several strategic locations you could have them do the pre-fab. They are starved for business.
You may also want to souce local quality installers if the homeowner wants an “Assist”. http://www.groundtradesxchange.com is a good forum for that.