They are usually very nice people to deal with but you will get a very low offer if you sell direct to them. As you state, they need to make a profit.
Sure, it reduces the hassle of selling, saves you the stress of your tax concerns, and they handle all the shipping of the item(s) to them.
But you lose significant value as opposed to what you could sell for online here or elsewhere.
What have you got to lose? Send them the info and photos of what you want to sell and see what they offer. In my experience, the low price was not worth the loss of $$ in my pocket.