HI all - looking for some thoughts / info. I see a lot of...

HI all - looking for some thoughts / info.

I see a lot of comments about people who are T+3 dumping ASX shares thus affecting shareprice afetr 3 days of rising. What does this mean - is it that generally the institution used for trading will not charge the traders the cost of the parcel only brokerage and any loss (or profit) incurred thoughout the transaction if done within 3 days? If so I am being done over by commsec I think as they said that the above only applies for same day/next day with my account, but 2 days if its a sell then buy situation opposed to buy then sell. Any commments / experience in this much appreciated..... Be gentle I am a newbie!