This is a bit of online-store etiquette that I'm not sure of - is it ok to make an offer on something in an online tack shop's consignment section? It's something I wouldn't hesitate to do in-store, so I'm not sure why I'm questioning doing it via email/phone!
You can always ask. I'm saddle shopping and saw one that was a bit beyond my budget, so I asked. They did come down a bit - I'm sure they have a number that the consignee has indicated is the lowest they'll go. I have no problem asking if there is room to negotiate.