Certificates are not the core asset in an account that includes an app
Buyers often rank certificates first, but the order should be reversed. A certificate in the developer portal is only the public side of a signing pair. Signing needs the private key, which normally lives on the Mac or CI machine that created the request. Seeing a certificate in the portal does not mean you can sign with it. Conversely, an expired, lost or revoked certificate can be reissued inside the account, and apps already on the App Store stay available. What cannot be swapped is the Bundle ID and the App Store Connect app record. A Bundle ID cannot be changed once an app record is created with it, and ratings, reviews, in-app purchases, subscription groups and the update channel for existing users all hang on it. Check the app record and Bundle ID first, certificates second.
For the Bundle ID, check the capabilities and what they depend on
Open each target identifier under Certificates, Identifiers & Profiles and note three things. First, whether it is an explicit ID or a wildcard, since wildcards cannot support push or in-app purchase. Second, which capabilities are enabled, such as Push Notifications, Sign in with Apple, Associated Domains, App Groups or iCloud. Third, whether the resources behind those capabilities are in your hands. Associated Domains requires control of the verification file on the domain. Sign in with Apple and push also tie into keys or Services IDs. If the domain, backend or third-party push provider stays with the seller or a previous team, the Bundle ID may sit in your account while the features still fail.
The app record state tells you whether you get a live app or an empty package name
Ask the seller for the App Store Connect app list and the version page of each app. Focus on four things: whether the current version is on sale, removed or taken down; whether any rejected or in-review version exists; whether in-app purchases and subscriptions are still approved; and whether the primary language, category and privacy answers are complete. An app that is on sale and was updated recently shows the package name is still usable. A removed or long-dormant record needs an explanation, whether it was voluntary, caused by agreement or certificate issues, or by a review action. Do not rely on a verbal answer. Any open review matter is determined by what the console shows at the time.
Separate what can be regenerated from what cannot: APNs keys and server config
An APNs auth key (.p8) can be downloaded only once, at creation. The portal keeps a record but cannot return the file. If the live backend uses that key and you do not receive the file, you will create a new key and change the server configuration instead of taking over as-is. The same applies to the .p12 for a distribution certificate and the private key for Sign in with Apple. List these in two columns before ordering: items that can be regenerated inside the account, and items that depend on files the seller holds. The longer the second column, the more important it is to agree in advance which files are handed over, which you rebuild, and whether production features are affected during the rebuild.
Team role and agreements decide whether you can actually operate the app
Even with the Bundle ID and app record in place, confirm who is the Account Holder and whether your role can manage apps and agreements. In the Agreements, Tax, and Banking section of App Store Connect, an unsigned Paid Apps agreement stops in-app purchases and paid features from working, while a free app without purchases is not affected. Ownership and handover of that area is covered in a separate article. The point here is that the check depends on the app's business model: a free utility and a subscription app need completely different agreements and payout items confirmed.
When a clean aged account is the better choice
If you only want an account with some age to publish a new app, taking on someone else's Bundle ID and history adds variables you do not own, such as naming, old reviews and review records. An account with an app is worth it only when you need to keep a live package name and its users, when in-app purchases or subscriptions have an existing user base, or when you must keep existing ratings and reviews. Stop signals are clear: the seller cannot show the app record in the console, cannot explain what the Bundle ID capabilities depend on, or scopes delivery to login details without mentioning the app record and key files. If the app already sits in another account, an official App Transfer may be an option, but eligibility follows Apple's page at the time and should not be assumed.