If the customers are from US you can easily suggest them to use Coinbase itself. As for others you can suggest them this website to search for exchanges in their country :
http://howtobuybitcoins.info/ and
www.localbitcoins.com is almost available in all the countries, so that's another option. And other than that, tell them to email you if they need help and you can help them on case by case basis.
If they need more resources to understand Bitcoin, just suggest them this forum or the Bitcoin site :
https://bitcoin.org/en/getting-started to help them get started.
Good luck with your business.