Every few months a business asks us to build something that already exists as a product. Sometimes that is the right call. Usually it is not, and it is worth being honest about which situation you are in.
Default to buying
An established product has absorbed years of edge cases you have not thought of yet, has a support team, and gets security patches without you commissioning them. For genuinely common needs such as accounting, email marketing, basic e-commerce and payroll, building your own is almost never justified.
The standard objection is that the product does not do things exactly your way. Before treating that as fatal, check whether your way is a deliberate advantage or simply the habit that formed around whatever tool you used before.
Build when the difference is the point
Custom software is warranted when the process it supports is part of why customers choose you. If your quotation logic, your scheduling constraints or your service model is genuinely unusual and genuinely valuable, forcing it into a generic tool erodes the thing that makes you competitive.
It is also warranted when you are stitching together several systems that will never integrate properly, and the connecting layer is where your actual workflow lives.
Then check the arithmetic
Per-seat subscriptions scale with headcount, and the cost of a growing team on several products at once adds up faster than people expect. Add up what you pay annually across every subscription doing a job custom software could cover, then compare that against a build cost amortised over five years, including maintenance at roughly fifteen to twenty percent a year.
Often the honest answer is that buying still wins. Sometimes, at a certain size, it clearly stops winning.
The middle path is usually best
Most of the good outcomes we see are hybrids. Buy the commodity parts such as accounting, mail and storage, then build only the specific piece that carries your competitive difference and connect it to the rest by API.
That keeps the custom surface area small, which keeps maintenance small, which is what determines whether the system is still useful in five years.
Two questions before you commit
What happens to this system when the person who understands it leaves? And who owns the code and the data if our relationship ends?
If either answer is uncomfortable, sort that out before writing a specification.