As an IT consultant, you should know most PC vendors would be happy to cover inexpensive items like a mouse under the standard warranty.
However, given that your client could purchase a spare replacement mouse for about $10 to $30, is it really worth one of their employees being without a mouse, or worse yet without a PC, for a day or two while they await the replacement part under standard PC warranty coverage?
Clients Should Have Spare Parts on Hand
If your clients have spare mice on hand, warranty claims can be deferred a few days, or a few weeks, until time permits. In the interim, as their IT consultant, you