The number in the proposal is never the full cost of ownership. Budget for infrastructure, paid APIs, observability and a change budget for every year the software runs.
Brandieritte
Ask where their numbers come from. A credible estimate is accompanied by a list of assumptions, a breakdown by feature or module and a best case and a worst case.
Be wary of a gap between the engineers on the sales call and the people who will code. Ask for named engineers in the agreement, with a clause about substitutions.
The number in the proposal is rarely the full cost of ownership. Plan for hosting, third-party licences, monitoring and an ongoing support budget annually.
A quote that comes back within a day is a red flag rather than good service. A competent team responds with questions first: about integrations.
Require access to the repository from the start. A team that delivers nothing between demos expects you to accept a black box. Daily commits reveal the actual pace far better than any status report.
In the real world, companies blend them. A common pattern puts architecture, product decisions and core domain code in-house, while an external team handles the parts that are bounded and specifiable.
Third-party integrations are the second big multiplier. A feature that touches only your own data is low risk; the same functionality connected to a legacy ERP is another matter entirely.