We have multiple brands in different verticals. Should I open separate Sift accounts for each of them?

Fraud can vary substantially across verticals. Each Sift account comes with its very own fraud prediction model, so you’ll likely get best performance from having a separate account for each site. 

With that said, volume is important and each situation is a little different. Contact our Sales team and we can discuss best practices.

We have the same brand in multiple geographies. Should I open separate Sift accounts for each of them?

If each site operates in a similar vertical with similar offerings (e.g. amazon.com vs amazon.co.uk), then keep them under one Sift account. You'll want to add a custom field to capture which brand users are operating in. Use a term that makes sense to you and send the value as either an integer (e.g. for 'brand_id') or a string (for 'brand_name'). Add it to the event you perform a risk check on (for example, $create_order, $create_content, or $create_account).