Hi, and welcome to the site!!! First off, I would stop taking advice from the salesperson. A mushrom anchor is all but useless with the excpetion of a 12 ft. aluminum rowboat, and even then only in calm conditions. A Danforth if probably one of the most common anchors, but Dan Barry will not be happy if he has to hold your boat in place for more than a few minutes.....particularly if you don't have an anchor.
What belongs in your anchor locker is an achor and the anchor line. Danforth's are popular because they are basically flat and will lay ontop of your anchor line and fit nicely into the anchor locker.
The key questions are:
1) What is the bottom like in the areas you plan to anchor?
2) What is the wind, wave, currents, and/or tides like in the area you're achoring?
3) What will you be doing when you're anchoring?
4) How long do you intend to anchor?
Most folks want to pull up to a beach or sandbar, toss out the anchor and swim and enjoy the day. For that boat, the most common would be a Danforth. They hold very well in a single direction. Most folks get a second much smaller danforth and back up to the beach. The larger anchor goes off the bow and the second smaller anchor goes off the stern and holds the stern to the beach and the bow towards the open water.
Stay away from Mushroom anchors, grapnel anchors, whacky box anchors.