If you comply with the rules of the profession or trade that apply in your own country, you can, in principle, offer those services anywhere else in the EU.
Fe ellwch felly deithio i helpu cwsmeriaid mewn gwlad arali neu fe ellwch ddarparu gwasanaethau am dal o'ch gwlad eich hun heb orfod teithio yno (er enghraifft, trwy roi cyngor i gwsmer dros y ffôn neu'r ffacs).