In today's environment there are many times when a host will unknowingly host a fraudulent website, such as a fake courier website or phishing site.
As a reseller, you need to be careful about who you sign up for hosting. during the ordering process it advisable to get the person's IP address and match it against their said country. you can check the location on a website like www.ip2location.com
Joomla: often has writeable folders ( sometimes because of the webmasters own fault) this allows fraudsters to host/upload fake websites which people will goto thinking it's their bank or they need to update their paypal contact details.
Keep your hosting username and password safe.
If you have any other advise please let me know it.