I think multiple bidding strategies or price comparison is inherently flawed for service businesses. It forces adverse selection on both sides. Essentially, to the buyer, all contractors are vetted, licensed, and have insurance, and they have no other context, so they are forced to choose the cheapest bid. However, the sellers (contractors) don't know what type of client this is, how much they might try to change scope, or what the actual project might end up costing, so they are forced to charge as much as possible to cover the unknown.
By forcing them to bid on the project, the better contractors, who are more aware of the potential costs and risks will bid higher than the less competent ones.
Essentially, this will skew the process in a way that the customer will always end up with the worst vendor.
Further, the contractor needs to confirm price upon inspection. If this leads to changing bids, as most industries do, either the customer will be too annoyed with your site and the contractor, or just go with the new bid...and contractors will quickly learn to bid low and quote higher on site.
I would love to hear your thoughts about this and how you hope to overcome adverse selection from a bidding model.
For what it's worth, I have my own ideas for the space, but they aren't technology driven solutions, they are people driven solutions.