@Daniel1992
I get a lot of requests similar to yours, i.e. someone who will be coming to London for a couple of days a week on a regular basis for work or study. I don't mind that they ask for a discount or special rate or think they would be bad guests, because I can see why they might think that I would really want a regular, repeat guest over a period of time.
In fact, this might work very well for hosts that do not want or need their place to be booked seven days a week or who just don't get that many bookings. The security and familiarity of a [good] regular guest might be worth a discount.
However, I always politely say no, because it doesn't work for me at all. My rooms are pretty much fully booked year round, which I think demonstrates that the price is already fair. If I have two/three nights every week blocked off for a particular guest, I would potentially be losing a lot of other bookings (longer stays, more people etc.). It would involve more turnover for less income. Why would I offer a discount on top?
I'm more than happy to give a discount to long-term guests though. That's different, because they are filling my calendar, not leaving it full of awkward gaps.
The other kind of request is the short-term, one-off guests who think they should get a discount just because they are asking. I get these all the time too and the answer is always NO. I think this is more the type of guests that hosts refer to on the forums as likely to be trouble. I'm sure that's not always the case, but I don't see why I should give a discount for no discernable reason whatsoever.