We can't upload more than three Image, but we have also addition two for pdf where you can upload your proof of work, PDF will attract your buyer, they will know what kind of services are providing them.
Other seller might have image more than 20, but those aren't upload by the seller. When you deliver your order you will get option to upload proof of work, there will be option to share those proof with people, by default it might not be enable. Please be careful while selecting those thing because if you are delivering sensitive or personal thing that will not be good for buyer.