Fixed price tradesman services. Would you use this?

I’m currently working on a booking and payment service to facilitate fixed price trade services.

I’m trying to fix the variable pricing involved with trade services – electrical, plumbing etc. Fixed prices are aimed at providing a price guarantee for customers (i.e. not being ripped off) whilst giving some price assurance for the tradesman and both parties share some project risk.

Example: $200 to install a single power point within a 10km radius of (insert city) centre.
Example: $300 to replace 10 tap washers within a 10km radius of (insert city) centre.

Would you use this? Brutal honesty always appreciated.