It can get frustrating at time I know. I have dug up plenty of junk since I been MT-ing.
When I hunt. When I get hits, if I feel without a doubt that it's junk, I won't dig it up. but if I have a 50/50 idea it may be something worth digging, I dig.
I just metal detect for fun, so I don't really care if it's really worth bucks. I just have fun seeing what's in the ground.
One thing that may help you like it helped me was to jot down readings when you hunt on what your MT tells you on a hit. Both display and sounds. Be sure when you "X" the spot, that you move yourself around in a little circle to "X" it from every angle. Then what ever you dig up, jot down next to your readings you recorded on what the object was you got. Over time you get much better at figuring out if it's worth digging up or not.
I been metal detecting for maybe 4 years, and found that if you play around allot in your back yard or a field with all kinds of different metals of your own, burying them at different angles, depths, and with different types of metals, then "X-ing " what you know is in the ground, it really helps to ID the stuff when you don't know what's in the ground somewhere.
So if you can. Take a bunch of objects of all kinds of metals and go put them in the ground and play, and play, and play. I bet in a month or so, you will be able to distinguish your hits a hole lot better. (pun intended)