Speaking of "Round" in the sense there are 5 total Rounds in the game, then you are allowed to buy wool during Round 1, then sell wool later in Round 2.
However, you are NOT allowed to buy wool early in Round 1, then sell wool later in Round 1. As it clearly states on page 4 (bolded, in fact):
It is prohibited to have Merchants from the same player on both the buy and sell area of the same Good.
As the OP stated, he knows you can't buy and sell in the same round.
If I sell wool early in the round may i return to sell wool later? I know you can't buy and sell in the same round.
This is specifically about selling and selling (or even buying and buying) in the same round.