Ensuring accuracy of your data is critical to any analysis that follows.
When transcribing data from paper records to digital representation, have at least two, but preferably more people transcribe the same data, and compare resulting digital files. At a minimum someone other than the person who originally entered the data should compare the paper records to the digital file. Disagreements can then be flagged and resolved.
In addition to transcription accuracy, data compiled from multiple sources may need review or evaluation. For instance, citizen science records such as bird photographs may have taxonomic identification that an expert may need to review and potentially revise.
Manually entered data can suffer from a high error rate. Double data entry and/or double checking of data can dramatically improve data quality.