I agree...and wouldn't that be nice?!? Fortunately, SOME companies still believe in that.
Also, don't forget that YOU are a business. As an Independent Contractor (NOT an "employee", you don't just have to take the shop for what they initially offer. If the stated fee is not acceptable, you can tell them, "Sure, I'll do the shop, but since it is last minute and I'll have to rearrange my schedule in order to fit it in, I want $xx.xx to do it." Then, it's up to them to decide if they need it done badly enough to pay that. If not, you didn't have the shop to begin with.
Having said that, especially NEW shoppers, try to do some last minute shops at what they offer so that you DON'T get the reputation of an extortionist and DO get the reputation of being a shopper that can be relied on and who is willing to "help out" in a pinch. BOTH are remembered and shared with others...just like WE share about our experiences with different companies.