Now I’m obviously biased in my answer, being an audio engineer and all, but think about it? You’re putting your mixtape online on sites like Datpiff. Imagine what people who have never heard your music are going to think the first time they your songs? Are they going to say, “Wow! This is amazing!” and share it with their friends. Or are they going to say, “Yeah it’s okay. I wish he had got it mixed and mastered”.
If you’re not getting your stuff mixed and mastered, they’ll probably say the latter. First time listeners are going to see you as not only an amateur that shouldn’t be taken seriously, but they are also not going to spread your music to their friends on Twitter and Facebook. Why?
Because do you recommend things that are not good to your friends? Nope. Put yourself in the proverbial shoes of a first time listener? Why do YOU share music from other artists with your friends? Would you share something even if it wasn’t mixed and mastered? Probably only to make fun of it.
Your songs maybe “good” but if they aren’t mixed and mastered, people, especially music lovers, will say “yeah he has potential, only if he mixed his stuff better”. And you don’t want to upset this group of people.
You don’t get your mixtape mastered because you’re going to sell it (maybe eventually you will if it’s successful and you get a record deal like Drake) but you get it mastered to show the world what kind of artist they are dealing with. Either your somebody we should take seriously or your another wannabe.