Begin with relevant experience, not the size of the portfolio. Request three or four case studies that resemble your domain and your stack, and then ask whether those engineers are still with the offshore software development company. A serious vendor will introduce you to the tech lead. Vague answers at this stage generally mean the delivery team is not the team you were shown.
The contract deserves more attention than the sales deck. A few clauses carry most of the weight: intellectual property assignment, non-disclosure, and termination and handover. Everything produced has to transfer to you as it is paid vue js developers for hire, including designs, scripts and infrastructure configuration. Look closely at any clause that keeps framework code outside the transfer, because this is frequently the part you cannot replace later.
Find out how the estimate was built. A credible estimate arrives with a list of assumptions, a breakdown by feature or module and a range rather than a single number. A fixed-price contract works only when the requirements are stable and documented; in any other case the provider pads the number and you pay for it anyway. Hourly billing shifts that risk to you, so it demands a sprint cadence, demos and a budget cap.
Process matters as much as headcount. Establish how a new requirement enters the plan, who writes the acceptance criteria and how quality assurance works. A team will be able to walk you through a live build at the end of each sprint. Written acceptance criteria stay your only real protection against endless rounds of rework.
Last, plan for nextjs development agency the handover before it becomes urgent. Insist that the repository sits in your organisation from day one, and that the documentation is refreshed in every sprint. A provider confident in its own work says yes immediately; resistance at this point tells you quite a lot.