Middlemen do serve a valuable function - at times that is.
Here are a few scenarios, where you as a middleman can be reasonably sure that your customer wont’ circumvent you:
Your job is to coordinate production runs between several producers, and require that more than 2 producers have to deliver complementary products at the same time. (most US or European mid size importers can’t be bothered coordinating that while not on the ground)
Your commission is seen as insignificant by the paying party. (If their margin is 200%, and you demand 5% - and he customer sees you as adding just a little bit of value, your job is fairly secure)
You show you have value by ironing issues out fast and efficiently. (If the customer has a quality issue, and he has to communicate it to Chinese or Taiwanese who as a rule will try to avoid admitting to screwups and don’t have a great grasp of English to boot, then you have a relatively stable gig going)
The product is fairly complex and requires quality control at several stages. (You are the customers eye and ears on the ground - and you are cheaper than sending staffout here several times per year, then you are OK).
If the customer needs a whole industry to be monitored, and buy from several sources. (Trade shows, factory visits, follow-ups, and other supplier identification is done best here, by people who can talk and understand the locals).
I have taken customers I more or less trust to see suppliers several times without any ill effect for my profits, rather the other way round. also don’t forget that for smaller importers, IE people buying for less than NT$100m per year spead over several products, you are the cheapest option for sourcing efficintly there is. Also don’t forget that you being here and talking the talk/knowing the locals and spending time with them should be able to get savings, which basically means that you are paying for yourself - while a few Taiwanese or Chinese suppliers will try to screw you over, if there’s not much in it for them moneywise, they won’t bother unless they don’t want to deal with you.
The key to the longevity of your sourcing/commission business is not on the Chinese side though. It’s on the western side. You have to be very clear about and explain what value you deliver to the customer, offer advice and guide them thru the jungle here. If the customer perceives that you are earning your keep, they are likely to keep you.
I have had 2 suppliers trying to bypass me. How did I learn about that? simple, the customers wanted to know why they were getting Chinglish emails, and what the f**k was going on.
As mentioned before, making sure that you are delivering more than 1 product to a customer helps. My best sourcing business customer is currently getting products from 2 suppliers, and that will double over the next months, and most likely double again over 2-3 years. In case he screws me over on 1 supplier, he will be left in the dark on where the rest of his products are actually coming from.
But in general, if you are perceived to deliver value, you will have more buying agent business walking in the door than you can handle.