Begin with proven experience, not the size of the portfolio. Ask for two or three projects that match your domain and your stack, and then ask specifically whether those engineers are still with the ecommerce software development company. A serious vendor is happy to connect you with the tech lead. Vague answers at this stage almost always mean the delivery team is not the team you were shown.
The contract needs a slower read than the pitch. Three clauses do most of the work: ownership of the code, confidentiality, and termination and handover. Everything produced should transfer to you as it is paid for, including designs, igaming platform development scripts and infrastructure configuration. Watch software development company for startups wording that keeps reusable components with the vendor, as it is usually exactly the piece that locks you in.
Ask where their numbers come from. An honest estimate arrives with a written set of assumptions, a breakdown per feature and a best case and a worst case. A fixed price only makes sense when the scope is genuinely frozen; in any other case the supplier adds a risk premium and you fund the buffer regardless. A time-and-materials model moves the risk back to the client, so it demands a cap, regular demos and transparent reporting.
How the work is run matters more than the number of developers. Establish how a new requirement enters the plan, who defines done and how testing is organised. A mature team will be able to walk you through a live build at the end of each sprint. Written acceptance criteria are the practical protection against endless rounds of rework.
Finally, consider the day you no longer need this vendor before it becomes urgent. Require that the repository sits in your organisation from the beginning, and that documentation is written as you go rather than left to the end. A vendor with nothing to hide will agree quickly; a long negotiation over it says quite a lot.
