Why would anyone force their beliefs on another person. My co-worker celebrates Christmas and is likely a Christian, but the point is to be respectful of all points of view. There may be a reason for debate but it is not in a customer/vendor setting.
Some businesses have leaders who stand by their beliefs and push Merry Christmas on their customers. No doubt they have customers who appreciate that. But it is not up to employees to make that choice for their employers.
Happy Holidays covers all the winter solstice holidays. It is respectful of your beliefs and doesn’t shortchange mine.
Testifying is a great way to bring new people into the fold, but it is inappropriate to do it in a business setting.