This is maybe one of the most common questions we receive.
Sadly, there is no one-size-fits-all answer here, but there are some things you can do, and some pitfalls to avoid:
- Do not use "industry data"
- Do not use "gut feel"
- Do not use "this is what we did last year"
Benchmarks
Instead, compare to a benchmark forecast.
As the above topic specifies, the only real thing you can do to see if your forecasts are doing well is to see if they are beating a simple benchmark. If your manual or auto forecasts are beating a baseline forecast in accuracy by 10% or more, then you can be confident that you are doing a decent job on forecast error for your products.