There is no way to stop customer finding out about Domain registrar but it is possible to hide company information you resell for. For example if you signup for Enom reseller account then your customer will always see Enom.com as domain registrar and you as the company your customer purchased domain from.
There is still a possibility customer might move to the domain registrar directly if registrar offers cheaper pricing then you being the reseller. In that case you should always resell for registrar who doesn't compete directly with reseller in pricing.
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yeah with most reseller programs you can put your info on top or bottom of the whois info which shows YOU as domain registration provder
but you cant hide it 100% unless you're an icann accredited registrar which costs $xxx,xxx to be one
Bashar Al-Abdulhadi - KuwaitNET Internet Services Serving customers since 1997
Kuwait's First Webhosting and Domain Registration provider - an ICANN Accredited Registrar