What dealers are buying today and selling today is often NOT the best proxy for what investors or collectors should do, simply because their time horizons are radically different. If your goal is to be a market marker (first change your name to Hi-ByePanda) in which you have a bid and ask out for many coins for every moment in time, then you will tend to choose coins that are readily available (MS67-68) and are liquid (being marketed by dealers as HOT, with no disclaimer that you are purchasing the bottom 25% of the coins that have been graded). If your goal is to make solid investment returns over 2-5 year hold period, then you will choose coins that are rare and at least MS69 grade (75% of all omp submitted grade MS69 or better on average, own the top 75% of graded coins, not the bottom 25% of the graded coins).
I rarely (less than 2% of coins sold) offer investors or collectors coins graded below MS69, instead I sell, dump, liquidate quickly to dealers these bottom of the grading spectrum coins, so I can recycle the money quickly into new purchases that have a 75% or better chance to achieving a MS69 coin. Another reason I don't want to sell low grades to collectors or investors is, if after 2-5 years they want to sell the coins back to me, I will have no interest in them, but if they want to sell MS69 or better coins I will at least make an offer on them. Finally, I don't like to sell coins to investors and collectors that I don't feel comfortable owning myself, I sell coins I believe in and avoid selling coins that I feel will provide subpar returns.
As in all things in life, there are exceptions. Sometimes you can't afford to buy a MS69, but you still want to participate in the market, in this case buying rare or undervalued varieties, mints or key dates may still provide excellent returns, not as great as a MS69 return or as liquid as a MS69 coin, but better than most other investments that are available for those with limited investment funds.