Custom development (contracting) your already guarantee the sale since they are paying you for what you already want so in that case I guess you could perfect your craft.
On the open market there is the trade off of no wanting to waste your time on what people don't already need.
In the case of the windows app you had validated your idea so at that point polishing it wouldn't have been that bad of an investment.
I guess the hardest part about these stories is as they say "hindsight is 20/20"
hmmm, sounds similar to myself at times. I think for me its an obsession with perfection. Hard to keep a balance between that and the pressure from non technical people to "Just ship it"
For the low trust issue, I think it is becoming more clear with the rise of blatantly fake content online. I think a good lesson could be learned in what formalities you should get in place when working with others to prevent getting screwed over. I myself have been screwed over before by business partners and learned that you really need everything in writing and often lawyers.
For the windows app, did you just not have the time to fix all the issues? Or was it the weight of responsibility in what the app did?
... Perhaps I am just not getting enough traffic yet for it to work. I had signed up for Amazon affiliates but they closed my account due to lack to sales.