I used to work for a consultancy that specialised in a very niche area (I won't say what – this is traceable enough already!). We charged our clients a very high hourly rate, because demand and supply. All the time I'd get calls like the following:
"Please could you just make this small change to the deployment?"
"Yes, of course. You don't have any contract hours left, so I'll just forward you to our billing department so you can sort out the payment first"
"Ah okay, please can you tell us how to do it"
[Even if I explained it, you wouldn't be able to do it – that's why you're coming to us.]
"...or better yet, just do it as a quick fix outside of work?"
[So... work for no pay? No thanks.]

While my company always had my back on these requests (obviously, they wanted payment too), they were so frequent that I got sick of it.