Vendors with "Call Us" pricing are not currently being merged pending a change that will move them into their own table.
A common error with PRs is a miscalculated percentage. The site uses a "percentage increase from base price model" – that is, a $5 -> $10 markup is a 100% increase, not 200%. I'm hoping that a unit test will catch these, but writing a guideline is quicker.
It's fiddly to get right first time, so here's the convenient formula:
(Higher Price - Lower Price) / Lower Price * 100