Nowadays, IT customers are becoming increasingly discriminating
{about/with their
purchases}.
(usage example from ‘Strategic Management’ By H. Igor Ansoff, via Google Books)
Discriminating adjective (see especially definition 2a):
1: making a distinction : distinguishing (a discriminating mark)
2: marked by discrimination:
a : discerning, judicious (discriminating buyers) (emphasis added)
b : discriminatory (accused of discriminating practices)
(from Merriam-Webster)
Regarding your passing mention of “shrewd” (which I don’t interpret as your final decision to preclude it as an option), notwithstanding my answer above *(and the caveat mentioned below), I think it would fit well in your context (and by changing “becoming” to “getting,” you could even add some [admittedly lame] wordplay to the first sentence!):
Tired of getting [increasingly] screwed, nowadays IT customers are
getting {increasingly}
shrewd
[at negotiating prices].
(example usage from ‘Labour and Gold in Fiji’ By Atu Emberson-Bain, via Google Books)
Although you’d need to (unfortunately?) go back to “becoming” (and miss that wonderful wordplay opportunity?), I think it would also fit as part of the following two-word option:
Nowadays , IT customers are [increasingly] becoming [increasingly]
shrewd
negotiators.
(example usage from ‘Open Sources 2.0: The Continuing Evolution’ By Chris DiBona, Mark Stone, Danese Cooper, via Google Books)
Shrewd
Function: adjective
: showing quick practical cleverness : ASTUTE (a shrewd observer);
also : marked by clever dealing that takes advantage (a shrewd negotiator) (emphasis added)
(from ‘Merriam-Webster’s Student Dictionary)
*(Please note that the “takes advantage” part of the definition might make it less neutral/positive than you want, but people who I have called “shrewd” to their face have never seemed to take offense and have often seemed pleased.)