They're not special, they just have a lot of teeny internal passages that are difficult to clean properly. On top of that the diaphragms are delicate and expensive. I do all the work on my vehicles myself with rare exceptions, but chose to send my 250 carbs to Gordon recently because I've been very busy and wanted them done right the first time.
You know what it takes to clean them yourself, just don't overlook anything or you'll be doing the job multiple times.
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DannoXYZ has some labeled photos that show all the parts that need cleaning, maybe he'll be kind enough to post them for you.