SUNPAK 035C 35mm Electronic Thyristor Auto Flash with 35-85mm Zoom

I bought this flash insted of a canon flash hoping to save some money,it did not work.The flash would sync sometimes and other times it would think on it's own. I took it to two different camera shops and they told me in so many words that it has to be compatible with your camera in other words it has to mesh with the functions.