Citizen-science projects can collect far more wildlife observations than professional teams, but volunteers cluster near roads and cities and sometimes misidentify similar species. Discarding volunteer data would sacrifice valuable geographic and seasonal coverage, while treating every report equally would produce misleading abundance maps. Ecologists propose short identification training, photograph or audio vouchers when feasible, expert review of uncertain records, and occupancy models that account for unequal observation effort. Together these measures can use the scale of public participation while estimating where absence of a report means little. Remote regions may remain undersampled, expert review can become a bottleneck, and some valid observations cannot be documented with a photograph or recording.