Testing theme before buying

So, I am interested in purchasing a theme, as I have had a lot of trouble using Debut on Shopify. I am already extremely disheartened as Debut is described as being optimized to mobile and desktop, however, there is no way of having different settings for the images for mobile and desktop, so it’s impossible to have what you want for both.

I’ve created beautiful designs which I cannot use on Debut. If Debut had different settings for mobile and desktop, the banner would look amazing. But I have to have to same sizing settings for both, which means one looks all wrong.

So I’m interested in purchasing a theme from your website, however, what I don’t want is to buy it and then find that it doesn’t do what I want, just like Debut.

Is there a way of testing out the theme before buying? I don’t understand why anyone would take the risk and pay money for something that doesn’t work like it said so; just like Debut. Seeing the examples of ready made desktop websites does not help me.