Hi Allen, Re: Commission cost as a percentage of Order Value......
Generally I used to attempt to keep the commission cost at less than 1% of the trade order value. That would mean a $1000 trade as a minimum at TD. To go from your current trade amount of $185 to $1000 would probably put the "next sell" price well beyond its suggested sell price/share and negate the trade.
Remember that you pay commissions in both directions, so 5% in each direction would eat seriously into your overall profit. Keeping track of the gross and net cost on transactions will help guide your hand. Ameritrade's Gain/Loss page can help, too.
If you and AIM are making just $15 on the trade and AMTD's making $10, that's not a great ratio. :-) Of course much depends upon the way you calculate profit - LIFO, FIFO or Average Cost. We talk about AIM's LIFO gain target being ~20% to 30% generally, but we don't pin that down to dollars very often. That would be ~$100 to $150 on a $500 trade. Even there the $10 commission is a big chunk of the gross profit.
So, order size matters on commission based trades. There are some "fee based" brokers around and if you're a day trader they might work okay. To pay 1% to 1.5% of the value of the portfolio annually as a fee would require a lot of transactions to pay for itself, but if there were going to be dozens of small transactions it might work.
Over the years I think I averaged less than 1% total commission cost on a round trip basis. That required trade values above $2000 per transaction if I remember correctly.
Hope this helps.