If I understand correctly how this works this could potentially help you to get an advantage over other goldmakers but it could hurt you as well.
GuildOx will apparently try to match up your characters by comparing Achievements which should be the same on all your characters thanks to the account-wide achievements.
How can this help or hurt me?
Linking Bank alts to main characters can help you immensely in your gold making efforts (see PhatLewts’ Post about the value of keeping tabs on your competition).
If you know your main competitor is in a progress guild and will be raiding during certain hours you can take over the market in that timespan which gives you an edge over him or her.
But as I already mentioned this feature is a double-edged sword and can hurt you as well.
How can I avoid being hurt by alt detection?
It’s actually pretty simple, as GuildOx describes in their post you just have to check the “Display Only Character Achievements to Others” option in your Interface/Display menu ingame.
That will prevent Guildox from linking your bank alts to your raiding mains.