Absolutely! I've purchased many items from other users on here from corals to pumps to lights. Made alot of friends that way too.
Just be sure to stay safe when doing so. Always pay with Paypal Goods And Services in the unfortunate event something does happen. You are protected
I've never had a problem. You can usually get a good sense of a seller's item quality but reviewing current or past for sale threads and seeing what type of feedback they give. A lot of top-notch, straight shooters on this forum. As Crabs said, use a secure method of payment if dealing sight unseen and having items shipped.