Especially just buying tickets.
I got to travelocity, orbitz, and a couple of individual airlines looking for the best price/time of day combination. Travelocity in particular pissed me off this time for offering one price, which was the lowest I could find, and then being all "oh no oops the price just changed" by the time I got through five screenfuls of form-filling and no-I-don't-want-a-hotel-booking bullshit. And then I searched for the same flight again, got the same low price initially advertised, and then the same "oh no oops" message.
Travelocity, I don't believe you are making a benign error every time. You are plainly lying to me about the price of the service you are selling me, until I am at the very point of committing to buying it. And this doesn't even cover the extra $40 of fees that absolutely everyone tacks on at the end.
Ugh it's such bullshit.