Replying to [Amore]:
From you essay, I suppose you are a small dealer, so the quantity of your orders would be small. A small dealer always needs following support:
1.How to select the vendor?
You can't choose very big manufacturer as your partner, you ought to know that big factory needs big orders. They wouldn't like to do business with you, though they provide the best price.
As a small dealer, you need very good service, including high reponse speed, high quality products (if the quality is good enough, why should we need Guarantee?) and so on...
2.What is the best way for shipment?
Shipped by air would be the best, for the value of electronic goods are high enough, and their prices are changing very quickly, you can suffer the delay for time of ocean freight.
3.What is the cost for shipment? Between Europe and China or Korea
Different weight of goods, the freight would be different, you can refer to DHL, Fedex, TNT price list for shippment.
4.How the Guarantee will work?
Please refer to the first answer.
5.Does the customer need to pay extra cost for the custom?
Check with your forwarder or customs in your country, they would tell you.
I have full experience in exporting, if you wish, i would be very glad to cooperate with you.