It depends, but I think in most cases, it’s a good idea. Or put the prices on your website and link to that from Facebook. It’s not always possible to have fixed prices on certain items, but if you have specific rates, you might as well be transparent about that. For the price-sensitive customer, they’ll appreciate it, and for others, it will (at worst) be inconsequential. Perhaps there is some theory that if you don’t list the price and force the customer to contact you, you’ll get them in the door and they’ll be more likely to buy when they hear the price, but I think the reality is that most people won’t bother.