Ecommerce proposals are hard to compare because they bundle configuration, custom work, content and integrations in different proportions. The total is the least useful figure in the document, and the exclusions list, which most bidders will only produce when asked, is the actual proposal.
Ask e-commerce web developers for the configure to custom ratio
Ask each bidder what proportion of the proposed build is configuration of a platform and what proportion is custom code, and who maintains the custom part afterwards. That single question explains most price differences and most long term cost differences, because configuration survives platform upgrades and custom code is a permanent maintenance obligation you will carry long after the agency has gone.
Delivery promises are regulated
If you sell online in the US, 16 CFR part 435 governs what happens when you cannot ship when you said you would: it requires a reasonable basis for the shipping time you state, and sets out the notice and consent obligations, including the right to cancel for a prompt full refund, when you cannot meet it. That is a product requirement affecting checkout, order status emails and the refund path, not a policy page written afterwards.
Keep card data out of your systems
The PCI Data Security Standard applies wherever cardholder data is handled, and the single most valuable architectural decision is to use your payment provider's hosted fields or tokenisation so that data never enters your environment. That reduces what is in scope for assessment and shrinks your breach exposure. Require the card data flow to be written down and agreed before development rather than discovered during it.
Make performance an acceptance criterion for any e-commerce web developer
Ecommerce is one of the few places where a technical measurement maps directly to revenue, so it belongs in the contract. Google documents what a well built page delivers, including good Core Web Vitals, HTTPS, proper mobile display and no intrusive interstitials, all testable on any live URL including competitors'. Put targets on category and product templates and test them on real mid range devices at acceptance.
Questions people ask about e commerce software development services
How do we compare proposals from e-commerce development companies?
On the configure to custom ratio, who maintains the custom part, and the written exclusions list. Configuration survives platform upgrades; custom code is a permanent maintenance obligation you carry after the agency leaves.
What shipping obligations do we have?
Under 16 CFR part 435 you need a reasonable basis for the shipping time you state, and when you cannot meet it you owe notice, an option to consent to the delay, and the right to cancel for a prompt full refund.
How should performance be handled?
As an acceptance criterion with named targets on category and product templates, tested on real mid range devices, using the published page experience signals. It is one of the few technical metrics that maps directly to revenue.