There can be numerous instances where data needs to be cleansed and standardised.
To name a few -:
1) Mandatory fields having Null values - This is the greatest source of data loss
Remedy - Going back to the business, Replacing them with the mean.
2)Standardising columns- Like USA, US, America, United States.
Remedy- Using a lookup to change them to one standard value.
3)Date- This is one major issue where a file might have multiple date formats.
Remedy-This can be solved again by using a lookup.
4)Duplicates - This can be easily solved either in excel or in the database. You can even have a stored procedure for this.
5)Outliers- This is a separate thing all together, an outlier is a datapoint which comes from different distribution.I would suggest using the 3-standard deviation rules to mark potential outliers and then using a grub's test to check if they are outliers.
You can find cleansed and uncleansed datasets here https://www.datazar.com/
I hope this helped you.If you need any further details, feel free to email me at