Well of course, but I mean that as if you're not confident enough to recommend other engineers because of competition, then the root cause is probably your own standard of expertise that you have set that you have not met and should meet.
Personally, I don't think this is that big a deal. If you're a good engineer, there really is no shortage of opportunities. If you're not a good engineer, then that is the root problem that should be fixed. For me, recruiters are just people who helps me do the logistics work so that I never had to apply for a job.
"To this day, I don’t know what the recruiter said to my former manager, but I do know that my manager called me up pissed off about the phone call he’d received, and told me to not use him as a reference in the future."
I think that's a bad manager. As a manager, especially in tech, you should definitely expect your co-workers to take the best opportunity available. As a professional, the manager him/herself should also take the best opportunity available. It's people's careers, be professional about it.
I think that definition of "senior level of expertise" is a bit too much for full-stack engineers. I actually have worked with many engineers who are very comfortable working front to back end creating wholistic solutions. To me, full stack engineer is someone who can design and implement a wholistic solution. If you can build a todo app, you're pretty much a full-stack engineer (a junior one and also depending on the todo app implementation).
I'm not familiar with the extension, but you can build your own using their sdk. Extensions and auto-generated options usually have intrusive design choices.
I'm not so sure about this. Customers already are familiar with purchasing on Amazon. So if anything, Amazon increasing advertising for your product will only increase demand for that product. And that same customer who made the choice to purchase at your store should still purchase at your store since that choice was there to begin with and they already chose your store.
The only difference would be if that customer was not familiar with Amazon's offering prior to purchasing at your store. But only until we get concrete numbers and evidence can we conclude if that number who will be driven to Amazon would balance against the customers who are driven by advertising for more demand towards your store.