Merging Records in Mass

I thought Guest Checkout was smart enough to detect if there was already an account for the customer (if email matched).  Is that not the case?

No, not in our case.  Multiple records are created with the same email address.  

Guest Checkout is a scourge on our process, but here it is such as it is. First automatic merges are scheduled based on matching names and postal addresses. Also, member orgs create requests via CSIs, which are scheduled manually.   Between scheduling merges and processing them, a weekly scheduled merges report goes out to all the orgs to give them a chance to review and request changes such as switch keep and delete.  That report includes organizational constituencies, so most orgs just look at the merges for their own constituency. Finally the merges are processed weekly.  Repeat. 

Additionally, there's quarterly review based on duplicate emails on multiple accounts in a similar process.  Because of logins, and guests for orgs that allow it, duplicate emails are trickier. 

Wow.  We used Guest Checkout, briefly, a while ago.  We'd had some other issues with it: no way to turn it off for things that should require an login, like memberships and digital content was the main thing.  But we also have a  (Consulting-built) auto-merge system, so I guess I didn't notice.

Other integrations we've worked with have simply looked for a login with the same email address as the one entered by the customer, and considered it a safe assumption that this was the same person and therefore there was no need to create a new account.  It would be nice to have some kind of flag on the order itself (not the customer) that the order was executed using guest checkout.

Wow.  We used Guest Checkout, briefly, a while ago.  We'd had some other issues with it: no way to turn it off for things that should require an login, like memberships and digital content was the main thing.  But we also have a  (Consulting-built) auto-merge system, so I guess I didn't notice.

Other integrations we've worked with have simply looked for a login with the same email address as the one entered by the customer, and considered it a safe assumption that this was the same person and therefore there was no need to create a new account.  It would be nice to have some kind of flag on the order itself (not the customer) that the order was executed using guest checkout.