Yes! When you upload images to Picfair you always keep the copyright to your images, and you are free to do what you wish with your images, as well as having them on Picfair.
When images are purchased on Picfair, the buyer is not purchasing the copyright, but instead, they are purchasing the image on a licence basis. This means that a licence is purchased in order to use the image and that the image can only be used as stipulated within the licence agreement. These are in place to protect your copyright and to prevent buyers from using your image outside of the agreed terms.
Images on Picfair are offered with three different licences and you can see a full breakdown of the licences here https://www.picfair.com/licences