Short answer: locked at creation, so a mismatch means rebuilding
Google Ads asks for country, time zone and currency when an account is created. After that, those two settings are read-only in the normal flow. Wording and exceptions follow Google's help pages at the time, but there is no standard step to fix them after purchase. So when buying an account, the real question is whether it already fits. If a seller says they can adjust it in the back end, ask for the platform documentation. If none exists, plan as if it cannot be changed.
Time zone affects more than report dates
The account time zone controls when daily budgets reset, how reports split days, and which hour ad schedules run. Offline conversion imports also need timestamps consistent with it; check the current documentation for the format. When the zone is far from your target market, you often see budgets resetting mid-afternoon for your audience, or Google Ads showing a different 'yesterday' than your CRM or GA4. The rule: if you run in one region, match that region or your reporting baseline. If you run across several, pick the zone your team reconciles in and convert schedules yourself.
Currency sets the basis for budgets, billing and reconciliation
Budgets, bids, invoices and reported spend all use the account currency. It also has to be compatible with the payments profile country and payment method. Available combinations change, so rely on what the creation page offers at the time. If your invoices, client quotes or finance books use another currency, a mismatch means ongoing conversion cost and exchange-rate exposure on the payer's side. Also note that account currency is unrelated to the prices your landing page shows to end users.
Fields to confirm with the seller before ordering
Ask for back-end screenshots, with sensitive details masked: time zone and currency in account settings; the payments profile country and whether it fits the currency; whether the account is standalone or under a manager account; spend history, unpaid balance and restriction status; and whether existing conversion actions were recorded under the current time zone. A manager account can oversee sub-accounts in different currencies and zones, and reports can convert currency, but the sub-account's own settings stay as they are. Rolled-up reporting is not the same as an adjustable account.
With aged accounts, history is an asset but not worth a wrong setup
An older account is valuable for its data, conversion actions, audiences and spend record, all tied to that account and not portable. That is why some buyers tolerate a bad time zone or currency to keep the history. Set a stop line instead: if either setting conflicts with your main market or settlement method and you can't live with permanent manual conversion, don't buy it. It can be acceptable when budgets are small, the use is testing, reporting is consolidated in a manager account, and the time offset doesn't disturb daily budget or schedule reconciliation.
If you already bought the wrong one
When settings can't be edited, the workable path is to create a correctly configured new account, usually under the same manager account. History, conversion actions and audiences have to be rebuilt, and learning starts again. Don't pursue unofficial ways to alter the settings through a seller or third party. They aren't stable and can create review problems. Checking before the order is far cheaper than rebuilding after it.