Off-the-shelf tools are the right answer more often than agencies admit. Here is the point where they stop being it.
Most businesses should buy standard software for standard problems. Accounting, payroll, and email are solved categories. The case for custom work appears when the process that makes you money is the process no product models properly.
Three signals matter. First, staff maintain a spreadsheet alongside the software because the software cannot hold a field or a step that the business depends on. Second, the same record is entered into more than one system by hand. Third, the number leadership actually decides on is compiled manually every month.
When all three are present, licence cost is no longer the relevant comparison. The relevant comparison is the operational cost of the workaround, multiplied by every location and every year you keep it.
A useful test before committing budget: write the process down end to end, mark each step as software, manual, or judgement, and count the handovers. Systems should be built where the handovers cluster, not where the software demo was most impressive.