This is probably the simplest method. To allow customer to open an account and link to your reseller account:
the simplest
Send both Internal and Web data key https://www.simplylookupadmin.co.uk/A2CustomerAccount/WebAccountCreateFromReseller.aspx?id=4
https://www.simplylookupadmin.co.uk/A2CustomerAccount/WebAccountCreateFromReseller.aspx?id=4
External Use (All Web Software used by customer) https://www.simplylookupadmin.co.uk/A2CustomerAccount/WebAccountCreateFromReseller.aspx?r=W&id=4
https://www.simplylookupadmin.co.uk/A2CustomerAccount/WebAccountCreateFromReseller.aspx?r=W&id=4
Internal Use (All Desktop Software and Web Software used internally within a company) https://www.simplylookupadmin.co.uk/A2CustomerAccount/WebAccountCreateFromReseller.aspx?r=I&id=4
https://www.simplylookupadmin.co.uk/A2CustomerAccount/WebAccountCreateFromReseller.aspx?r=I&id=4
Where 4 is your reseller ID given to you after opening a reseller account.
The data key is then e-mailed to the end customer. They should then be able to put that in their software to enable their account.
After opening the account the customer will have access to their own account. You will also have access too there accounts under the "Reseller" tab in your account.