I have a couple of places around me that will buy clothes outright too. Considering the only two experiences I've had with the other type of consignment stores were that they went out of business with my clothes on their racks I prefer the buy-outright situation!
First, let me say that it can be terribly humiliating to have a young, clueless, gum-chomping gal rifling through your precious, expensive, and/or quality clothing and then offering you a mere pittance for your items. Or worse--rejecting them! I've had to kind of just get over that. Do I want some cash or don't I? The clothes I'm getting rid of are leaving my closet either way.
That said, I find it helps to merchandise my things a bit. I bring them in on hangers, with some brands I know they like in the front. I arrange things in a capsule, or in outfits if possible. I've been known to pin scarfs or ties on blouses, for instances. I put like colors together. I clean up my shoes and bags and touch up any worn spots. My store would rather have cheap plastic shoes that look new than expensive leather shoes that look like anyone had them on for a few wears. Oh well. I've had to fight against getting an attitude with them by reminding myself that the girl with the Sharpie has the power!
Now that they know me, they give me 65% because my items sell fast. I could have more in store credit, but that's a crap shoot, so unless I find something I want while they're pricing my clothing, I just take my money and run. The last 4 or 5 times I've gone they've bought everything I had.