I haven't had any conversions in DP ads. Would it be possible to receive a refund of the $75 I put in?
If you have used the $75 for ads, you cannot claim the refund regardless the ads convert traffic into sales or not.
No! That's not the way it works, try to pull that crap to adwords and you'll see their answer! If you're talking about unused credits, then maybe that's another thing, but maybe not, depends on the terms of use, you know the thing we never read entirely when signing up..
Come on thats ridiculous, you need to optimise/split test things until you get sales, you signed up for advertising not guaranteed sales.