Just to clarify the advice in this thread to make it clearer,
A Reseller's Certificate (tax id) will be required by "wholesale suppliers", unless you are an international customer. In most cases, the "wholesale supplier" will not require a tax id in this circumstance. If they do still insist on you providing one, then you can use a tax id from your own national tax authority.
A "Reseller's Certificate" is required by US residents dealing with US suppliers only.
While some "dropsgippers" also require a "Reseller's Certificate", not all of them do. and Surplus Suppliers usually won't require any tax id. If in doubt, just ask the supplier to clarify for you.