Change one input at a time
Generate the same date at two different times, or the same instant from two distant locations. A genuine observer-based chart should show corresponding changes in horizon geometry or object positions.
Sources: U.S. Naval Observatory — Computing Altitude and Azimuth
Look for provenance
Does the maker explain which astronomical data, timezone logic, and coordinate system it uses? Can you tell whether the date and place are calculation inputs or just printed text?
Ask how uncertainty is handled
If the birth time is unknown or the birthplace is approximate, a trustworthy system should not quietly present the result as exact.
Separate scientific accuracy from aesthetic taste
A chart can be visually spare, ornate, symbolic, or experimental and still be computationally rigorous. The question is whether the claimed geometry follows the stated inputs.