I've seen an influx of shopping-style questions lately:
- Where can I buy _____?
- What options for ______ are available?
- Is there a cheaper version of ______?
Since the field of robotics involves actual shopping (versus something like mathematics or programming), I'd imagine that the majority of StackExchange sites don't concern themselves with shopping when it comes to defining "opinion-based" questions.
In other words, could we explicitly list shopping questions in the list of questions to NOT ask on robotics.se?