A number produced without questions counts as a warning, not a service level. An experienced provider will come back with questions first: about users and volumes. A vendor swift development outsourcing that prices with no clarification is guessing, and a guess resurfaces as a change order — and you will pay for it.
Watch for a gap between the engineers on the sales call and the developers actually assigned. Insist on named engineers in the agreement, with wording covering replacement. A hire dedicated team that will only describe a pool of resources and refuses to name specific engineers is keeping the right to assign anyone it likes.
Insist on commit-level visibility from the first week. A provider that hands over nothing between demos is inviting you to take delivery on faith. Regular commits and pull requests show you who is really on the project far better than a weekly report. The same holds for the build and deployment setup: if it does not exist, assurances about quality are just talk.
Loose phrasing around intellectual property is not an oversight. The agreement must state explicitly that all outputs produced under it become the property of your company upon settlement of the relevant invoice. Also check the jurisdiction and the payment schedule: a large upfront payment with nothing due in return for weeks eliminates your only leverage.
Last, pay attention to communication. Confirm what overlap you will share with your working day, which named person handles questions and within what time. Four hours of overlap generally works; none at all converts each small question into a twenty-four hour round trip. Unclear written communication in the sales phase rarely improves later.