The limits of any check
No checker proves that a link helps. It proves that a link exists.
Indexes differ. Ahrefs, Semrush and Majestic each keep their own index, and none of them is Google's. Search Console is Google's own data but samples and delays it. Use two sources and accept the gap.
If a placement we delivered is missing or wrong, tell us through your account page with the order number. For the budget side, the two plans show how to reserve cash for fixes.
Which mistake costs the most
The expensive one is the first on the list. Everything else wastes a few dollars, while buying for a dead story wastes the whole order.
Think of the news desk habit of asking "is this still a story tomorrow?" Apply the same question to the target page before opening the basket. If the answer is no, put the budget into the sequel instead.
The cheapest fix is a log. A simple sheet with the donor, order date, target URL, price and a note after six weeks turns hunches into data. Without it, a year of orders blends together and nobody can say what worked.
If you want example budgets to copy, the two-plan page is a good start. For what to do about a chain of links, see the tier 2 tree.