There's no standard as to which certificate issuers have their trusted root CA cert installed. If your clients don't have it on their machines (desktops, phones

There's no standard as to which certificate issuers have their trusted root CA cert installed. If your clients don't have it on their machines (desktops, phones, servers, whatever) it doesn't matter what you paid. My point was that the more widely-trusted issuers (meaning installed by default on the most OSes) can get away with charging more because they're more compatible. There's nothing stopping you from setting up your own root CA and self-signing, maintaining a full chain of trust if you build the certs right (I've done it; once you have the process documented well it only takes a few minutes) but unless the clients trust the lowest link in the chain (not the case for self-signed, and some cheaper issuers) you'll still get validation errors.