half hour rate vs full hour rate ?

i've seen it posted requently on
providers' ads and i either don't understand
why they push their that time/rate on a client,
or am i to understand that this is a quickie
to which you will not get the full service (bj,gfe,DFK,tit-sucking,rimming etc.)

the half hour rate always seem like a
choice of a RUSHED service vs a
take your time but pay my demand rate service.
i prefer to see just a flat rate whereas
i don't have worry about how much time  
i have,clockwatching to make me have to hurry
 up with BJs,anal sex before she
calls it quits. i'd be so concerned with the
infamous " c,mon up, cum for me" line during
our session that i just don't think i could
really relax and enjoy myself.

i recently turn away from a TG session because
she wanted to do 15 minutes for $100..LOL!
that sounds like a pure HJ, and that just
wasn't happening.

More and more, i generally tend to stick to
the girls with the flat rate.(while open to
compromising negotitations) The donation
presentation offer is mine,and the choice
to accept is is theirs. and i guess it goes
vice versa.

Book half an hour and tell her if we are enjoying ourselves, we'll go for an hour and you'll pay for the additional time.  (Sorta like paying for sushi a-la-carte and if you eat too much, paying the all-you-can-eat price.)  If she balks, walk; it's going to be rush.  This worked for me the one time I tried it with a GG girl.  She proved she was a slow builder savoring each minute. I upped the time to an hour.