I've not sold a lot of G3 ponies, but from my experience with G1 ponies, I would say style the hair and get good photographs with bright lights. Use a photo editor to crop and make the pictures as nice as you can. Just be careful not to create more problems like tail rust, frizz, worse tinsel, etc. As for accessories, I'm going to try and sell my ponies with all accessories. If you check out Ebay, the G3 accessories that sell are usually with a pony.
AJ