You got it right. When IBM and Accenture come knocking to negotiate the room rates. IBM is in the better negotiating position. By extending the rate to IBM, Marriott ABC gains some revenue from rooms that it didn't expect to sell. However, if it extended the rate to Accenture instead of IBM, it gets the cheap revenue from those five rooms, but it also has to extend the cheap rate for another 4 rooms that it anticipated that it would have been able to sell at a higher rate.

Some math (very simple case)...

Suppose most rooms sell at $200/nt and the hotel had 5 empty rooms on average. It's happy to sell those rooms to IBM at $100 to get an extra $500.

Thus the nine rooms in question made (4*200) + (5*100) = $1300

However, if Accenture gets all 9 rooms for $100, then the hotel only made $900.00 for the nine rooms in question. Clearly, even though IBM needs fewer rooms, it represents the more profitable deal for the hotel. For Accenture to compete, the hotel would actually give Accenture a rate of $144.

Now, if 4 additional people misuse the IBM rate bringing the total number of IBM rooms up to 9 per night, the hotel had expected to make $1300, is only making $900. Thus when its time to renegotiate, the hotel will quite possibly extend IBM the Accenture rate of $144.

So surprising enough, misuse of a rate is harms both the hotel and the rate holder.