99% of the buyers don't know how difficult( or we can say it's almost impossible) to deal with the steel mills directly,  because all steel mills always give priority to selling their products to long-term agents, these agents can buy 99% of the mill's whole capacity of every month.  So the steel mill never care one inquiry of 50tons, or 500 tons, or even 5000tons from the oversea market.

That's because some trading companies in China, who registered a very similar company name with someone steel mill.  And normally these trading companies say they are the steel mills / manufacturers, no matter you need carbon steel, or stainless steel, or other alloys,  they will always say: "yes, we can produce". But everyone knows, no one steel mill can produce all the different kinds of steel/metal actually.

Avoiding to be defrauded.

There are 4 ways as below maybe can help you.
(1) Checking the supplier's basic information in Chinese Language. Very basic point, every Chinese company has company name/address/business license certificate in Chinese Language,if some companies can not show this information in Chinese, then you must be careful, maybe they are the companies registered oversea, like Marshall Islands/ Cayman Islands,you even don't know who they are actually and where they are.
(2) Checking the supplier's Bank account details. We all know that no matter Chinese companies or foreign companies, normally we open our bank account in the same city with our office. If one company send their bank account in another different city to their office, or even in Hong Kong or Singapore,then you must be careful, many clients were cheated after they transfer the money to these kind of bank accounts.
(3) Never be attracted by the super low price. As we know, steel products are bulk commodities, the cost prices in China are very transparent. A normal company's quotation is unlikely to be more than 10% cheaper or higher than that of other companies because the steel cost is fixed. If you receive a very cheaper price, then you must be careful, the super low prices are normally FAKE prices.
(4) Checking the payment term. The cheaters companies always request 10%-30% deposit of the total order amount, but they never care about the balance, they can agree any payment term for the balance based on deposit. But they don't accept LC, which is the most fair payment term for both of the seller and buyer. Many clients were cheated after paying the deposit, the supplier don't reply email or answer the call any more, or they request to increase prices at least 30% or even 50%.