A quote that comes back within a day is a bad sign. Any serious team will come back with a list of questions: about integrations. A provider that quotes before understanding the scope is simply working from a template, hire dedicated angular developers and a guess becomes a change request later — on your budget.
Look out for a mismatch between the team in the pitch and the developers actually assigned. Ask for the names and domain expertise software development company CVs of the actual team in the contract, with wording covering replacement. A team that talks only about roles and never names specific engineers is keeping the right to assign anyone it likes.
Require access to the repository from the start. A provider that hands over nothing between demos is inviting you to accept a black box. Regular commits and pull requests show you the actual pace far better than a slide deck. The same holds for the CI pipeline: if there is no pipeline, assurances about quality remain nothing more than words.
Ambiguous phrasing around code ownership is not an accident. The agreement needs to state in plain terms that all outputs produced under it transfer to the client as they are paid for. Check also the governing law and the payment schedule: a large upfront payment with no milestone tied to it eliminates your only leverage.
Finally, pay attention to the working rhythm. Confirm what overlap there will be each day, who which is better vue or react expected to answer questions and how quickly. Some genuine overlap generally works; zero overlap turns each small question into a twenty-four hour round trip. Unclear written communication in the early emails will not improve later.