You are gonna usually pay more to get rewards and points - BRS, for example, is rarely the cheapest place to buy from. For MAP stuff, please buy locally. You might get a few dollars in points from a web site, but the product is the same price and it is better to keep your money local, IMO. The few local stores that I visit save nice livestock for me and call me every once in a while if a rare fish that I want is available that week - this is worth WAY more than points, IMO.
High quality used helps hobbyists who are getting out of the hobby and stuff. There are some risks, so I look to pay no more than 50 cents on the dollar for good used stuff since the warranty is usually gone or ending - most of the stuff that I buy lasts years and years out of warranty (tunze), so this is not a huge risk for me. Moreso of a risk if you are buying tech that also works to run a reef tank.