We've heard this too many times to count: "Vendor B is only charging $15 an hour, so we have hired them."
Wow! You're saving a ton over our hourly rates, right? Not so much...
Turns out that Vendor B sent along their junior technical team to do your work, and they spent 49 billable man-hours total fixing a problem that should have been solved in less than three by a more experienced engineer.