No good marketer can tell you what kind of conversion rate to expect as they are always testing to find out themselves. (Even the most tenured expert marketing geniuses often find that the ad that converts the best is not the one they'd expect.)

You can study what has worked for others, but at the end of the day the only way to answer this is to create a few variations of your ad, do split testing, refine rinse & repeat.

It all depends on the targetting you use and the what not. It is almost impossible to predict conversion rates anywhere.

Yeah just don't go too broad at first , target one country and specific age groups ,demographics and minimum bids and increase slowly according to what is going on there,this doesn't have a fixed formula the only key is test test test.Good Luck!

There are too many variables to guess average conversions

Make sure to use retargeting , this will increase ROI, no matter which form of traffic you are using

Thanks for the responses guys, so overall I'm best to pick a couple of popular products off my site and target those at first??