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No worries!

You just have to meet ASA guidelines and fill out a form for a licence. I'm pretty sure a non-UK resident could do it, so long as they're compliant with the gambling code - off the top of my head...

Do you mean general betting reviews/guides? Sure - I have a couple I use adwords on.

You need to get your site approved for gambling ads first btw, probably should have mentioned that earlier. It's just a form you fill in though.

Organic search, social media, referral traffic from other sites, being awesome etc...

Also, you can advertise gambling sites to UK traffic via Adwords on google.co.uk (if that's your bag).