So, you only worked on that one sample image… Nothing more? Because your initial comment didn’t sound like that was the case…
Also, I’d suggest that you don’t work on samples for prospective buyers. Instead, create a portfolio showcasing your previous work (on one of the websites allowed by Fiverr) and be sure to show a wide variety of skills and talent in your portfolio samples. If someone were to contact me and ask for a sample, I’d direct them to these portfolio samples of mine so that they can make up their mind based on what they see.
Ok, if you worked on only a sample and if the buyer did not return back to place an order with you, that would mean that the buyer was probably not impressed with the sample you sent them and that they didn’t want to give you the actual job.
So what? No seller can possibly impress every buyer! There will always be such kinda buyers out there who will never be satisfied with what you have to offer.
Instead of making a big deal out of it, just move on dude.