Thanks for your reply.
We are a LLC company established in Delaware, so the tax law we are asking should be according to the tax law of Delaware.
1. As I checked in the governmental tax website of Delaware, I see they mention "gross receipt tax" applied to the goods sale but the percentage is different depends on goods. Our goods is electronic product, so could you please confirm that we do not need to issue any gross receipts tax no matter we sell to local buyer (B to C) in Delaware or other states in USA outside of Delaware (B to C) or out of USA (B to C)?
2. Our client is an independent entity from Hong Kong, we provide marketing service to them using our LLC company to run the project in Kickstarter (crowd funding website). After collecting the fund, we pay back the money to our client after deducting the agreed percentage as our income. Do we need any proof for accounting/tax purpose to avoid any misunderstanding? We do have agreement to prove but no any invoice. Do we need to reserve any withholding tax for our client to pay to USA? Or that's our client's obligation to report to USA that they have income from USA?
3. So for LLC, the sole shareholder need to file a individual income tax, no other tax filing obligation, right?
4. Is there any administration regulation to avoid penalty? For example, in Europe, we need to keep various documents (PO, bank statement, transportation document, invoice etc) in order to prove to tax office to avoid any penalty.
5. Is there any invoice requirement from tax point of view when we issue to business (B to B) and end-user (B to C)?
6. Is there any invoice requirement from tax point of view when we receive an expenses invoices to be used for office cost deduction? For example, in Europe, the expense invoice must be issued with company's VAT nr./company name/address, then it is qualified as an office cost.
7. Does USA charge customs duty when we import goods to USA from China? If yes, where can I check the customs duty percentage?
8. As you mentioned, there is no VAT or gross receipt tax in USA but we do receive an invoice from New York city company, they charge us with sales tax.
9. When we import goods from China to USA, do we need to pay any tax in advance? In Europe, we need to pay VAT and customs duty (if any) in advance.
10. Is there any special tax issue we need to pay attention to when we are doing business in USA? If this question is too broad, maybe you can send me some useful links for me to read. I just want to avoid any mistake in USA.