Start with relevant experience, not the number of logos on the website. Ask to see three or four engagements that resemble your stack, and then ask specifically which engineers actually built it. A serious vendor will put you on a call with the people who would work on your project. Vague answers at this stage usually mean you are talking to a reseller.

The agreement warrants more scrutiny than the proposal. Three clauses do most of the work: assignment of intellectual property, the NDA, and notice periods and handover. All the work product has to transfer to you as it is paid for, together with designs, ecommerce development company scripts and infrastructure configuration. Watch for wording that leaves so-called reusable libraries with the vendor, since this is frequently the part you cannot replace later.

Ask how they estimate. A serious estimate is accompanied by the assumptions behind it, a breakdown by feature or module and an explicit range. A fixed-bid deal works only when the requirements are stable and documented; otherwise the vendor prices the risk outsourcing versus in house software development and you pay for it anyway. Time and materials puts the risk on your side, so it demands a cap, regular demos and transparent reporting.

How the work is run beats the number of developers. Establish what happens when the scope changes, who writes the acceptance criteria and what the QA setup looks like. A mature team should be able to demonstrate running software rather than status reports. Clear, written acceptance criteria stay your only real protection against endless rounds of rework.

Before signing, consider the day you no longer need this vendor before it becomes urgent. Insist that the repository sits on infrastructure you own from the first commit, and that a readme and architecture notes are kept current as the code changes. A vendor with nothing to hide says yes immediately; resistance at this point says most of what you need to know.