Very close to Olli Niemitalo's response: As long as the exchange takes place via open channels (i.e. not a private conversation), I do not mind if the person is going to get paid for the advice they receive.
If the exchange happens over open channels: Others might get benefited from it AND there is an open track-record of what happened.
From time to time, I've seen questions where it was obvious that the OP was being paid for their work and adjusted my answer, if I submitted an answer, accordingly. If someone is making money, I would like to be paid as well.
This is reasonable but difficult to apply (or "enforce") in a way that would be compatible or viable with SE. Because, if someone is making money....then.....why not SE charge for the use of a platform that promotes paid advice (?).
But, on a more positive note, I don't know how setting up a donation channel would work (or be perceived), in case someone would like to donate some form of currency in addition to upvoting / accepting an answer. But again, that must have clear Terms and Conditions regarding what is donated and with what sort of understanding.