If you use dupe accounts to buy from G5, remember not to overdo it, especially regarding your delivery address and hp no. If they found out too many orders got identical address and details, they'll simply cancel your order. They manually verify your order one, not automatically through computer. You dun want to get your order cancelled at G5 one, because it is a pain in the ass long and tedious process to get back your refund money.

my 11street experience
i bought a few things thru facebook login (not yet register at that time), applied the vouchers
then i register with my gmail, download the coupons as usual

for the coupons that u have used previousy, example 50% apps only discount
u can no longer apply it with your new account
same recipient should be ok, but address and phone number cannot be the same
so, use lah office address, with diff phone number
or use family member's name, diff phone number, same address

i was actually half sweating, afraid 11street verify based on credit card info, otherwise kena lor...coz the facebook "me" and the gmail "me" both have exactly same credit card details, billing address, etc...