Here I asked about interstellar trade in raw materials, possible under the right conditions if necessary but not hugely useful. One of the obvious spin-offs of this was discussion of trade in manufactured goods. Personal consumer goods are a non-starter due to transit times and the rate of cultural and technological divergence at this level.
Now I'm wondering, if we take it as a given that interplanetary vessels and the likes of O'Neil Cylinders, large-scale fully integrated systems (that require no complex material inputs after they're built) of almost any size in other words, can be shipped interstellar distances. AND. The technology around these objects is basically stagnant having peaked long ago. AND. The cost of buying, and shipping, such a system is less than that of building the industrial capacity and manufacturing it yourself, support and maintenance facilities are still needed as cost just the same but you need them if you want the artifact at all.
Is a long range purchase order effective or do you still do it yourself because the ability to do it is important enough to justify the added cost? I don't want an opinion on Buy or Build, I do want specific justifications for picking one or the other option. Also does it make any difference if a star system is buying the equipment to start manufacturing these things themselves instead of finished product?