Quality is actually really important - I find myself saying that a lot, but it's true. xD
If you can find a scanner you can use or borrow that would be your best option, but if you really have to do pictures, just make sure they're straight and well-lit. c: You can also crop them in a digital program afterwards to make sure there's no table or anything in the background.
And, unfortunately, sometimes the effort put in doesn't make much difference in how much they're worth in a place like this. I certainly understand - I felt terrible when I kept trying to open commissions in 2009 but no one wanted them. I just didn't have the skill to pull it off.
Just keep practicing, 'kay? c: You might try looking at actual dogs and drawing them exactly as they are - your own dogs, your friends' dogs.. any dogs. Maybe even go to a dog park and do quick sketches. It's a really great practice tool to observe things around you that you wanna learn to draw, and it works for just about anything.