As time goes on counterfeiters get better at making fakes. Lower-quality fakes are often easy to detect when compared with a known good coin or a good image of a known good coin but high-quality fakes are now a real concern. This page will attempt to list the diagnostics for high-quality fakes but cannot and will not be comprehensive.
Scrape below first downstroke of N in IND and behind the King's shoulder on the obverse, rim cud above N on IND on obverse.
1905 Half crown
Slightly bent I in QUI on the reverse.