Just sketches and ideas will definitely not work. The factory will definitely make decisions for you, and there is a high probability that they will "guess" in the direction of saving money and trouble. And if the specification sheet is vague, the factory will likely not refuse production. They will let you pay first before executing production, passing the risk on to you. This is the most difficult place.
You must prepare a complete specification sheet, otherwise if something goes wrong with the product, you will have no evidence to refute and you will have to bear all the risks yourself.
There are some details in the specification sheet that you need to pay attention to. Please bring tolerances to the size specifications of the product. For example, instead of writing "20cm", write "20cm ±0.5mm". Product material must be clear to the specific model, such as 304 stainless steel, not simply stainless steel. Every detail must be confirmed in detail. If you encounter details that the factory cannot do, just negotiate and communicate.
The last and most important step is not to talk about the details of the specification sheet apart from Ali Wangwang. Suppliers must be required to clearly reply in Alibaba Want:"Production can be carried out according to the specification sheet"; or sign the specification sheet and change the official seal.