Onboarding is a selection criterion, not admin
Corporate supplier onboarding routinely requires insurance evidence, policy documents, modern slavery or ethical sourcing statements, banking verification, system registration and sometimes an assessment questionnaire. Each is straightforward for a provider who has done it before and unfamiliar for one who has not. The difference shows up as a start date that slips by a month, usually at the point when your existing arrangement has already been given notice.
Treat it as part of the comparison rather than as paperwork to be handled afterwards. Ask each bidder directly whether they have completed similar onboarding, what the longest part usually is, and who at their end manages it. A provider with a person responsible for supplier registrations answers immediately. One where the owner does it between jobs will be slower, and should say so and where their process is likely to slow down.
