Eventually some all-grain brewers decide that a pump is a good idea. Rightfully so, I came to that conclusion whilst lifting 10 gallons of 180° sparge water. Not fun.
But here's where the confusion begins; although it doesn't have to be. Most homebrew stores sell the March 809 pump which is perfect for homebrewing---short of the fact that it has to be primed. While this is a common annoyance, with a little practice it's not an issue. It runs on 120V, has a maximum head of 16 feet and runs at about 8 gallons per minute (gpm). Notice the output pressure here is low as well.
So some homebrewers will start checking eBay and finding pumps of all sizes, shapes, and capabilities. Note: you NEED a pump that can handle boiling wort. And you DON'T need a pump that has an output pressure of 50 psi, unless you want wort sprayed everywhere and your couplings to leak. Not to mention 50 psi will make your lines move if they're not securely connected (much like nozzle reaction, sans nozzle).
Then you'll find the ones on eBay that have no plug, requiring you to hardwire it yourself. Hope you're good with electricity.
Another good feature about the March 809 is it's magnetic-slip impeller. This means that you cannot cavitate this pump. You can starve it, but it's not going to create enough power to start ripping molecules of water apart and dropping the vapor pressure in the pump. Why not? Because (1) it's only 1/4 horsepower, (2) the RPM of the pump is constant and cannot be changed, and (3) because of the aforementioned magnetic-slip impeller. Trust me. If you want to see a pump cavitate, go to your local fire deparment, ask the engine driver to try to flow their deck gun at 2,000 gpm from a 20' draft. And if he actually tries it, smack the f--- out of him and reconsider your homeowner's insurance.
In the end, by the time you're done buying the cheap, sketchy pump off eBay, adding in this or that to make it work, it's easier and nearly as expensive to just buy the 809 outright from either eBay or a homebrew store. Unless, of course, you like headaches.