A number produced without questions counts as a red flag rather than good service. An experienced provider will come back with questions first: about integrations. A supplier that quotes before understanding the scope is guessing, and the gap resurfaces as a change order — on your budget.
Watch for a gap between the people you meet and those who eventually appear in the repository. Request named engineers in the statement of work, with wording that requires notice before anyone is swapped. A vendor that talks only about a pool of resources and will not commit to individuals is reserving the option to staff you with whoever is free.
Insist on the source repository from day one. A provider that hands over code only at milestones is asking you to trust a black box. Daily commits reveal the actual pace far better than any status report. The same applies to the automated test suite: if it does not exist, quality claims are unverifiable.
Vague phrasing around code ownership is rarely an accident. The contract needs to state in plain terms that all deliverables belong to your vue.js software development company as they are paid for. Check also the governing law and how payments are structured: best aso service a large upfront payment with no deliverable attached takes away the only leverage you have.
Finally, examine how they communicate. Establish what overlap there will be with your timezone, who handles questions and on what response times. Some genuine overlap is normally sufficient; none at all stretches each small question into a lost day. Sloppy written English in the early emails does not improve under delivery pressure.