it happens. Embassies sell visa for $. Immigration doesn't work with Embassies. As said believe it or not I don't care but it's upto the IO of the day. If they don't like the look of you they will find a reason even ask to see the cash you must carry and decline entry if no cash visa or not.
Some one wanting to come in and out many times on visa or exempt is normally trying to live here. Very common hence why border runs and visa runs are also popular.
I go every month have done for years. I never been stopped but always have a return flight every 2 weeks. I also know the risks of eventually being stopped and questioned hence I got a retirement visa and still go every 2 weeks.
Refusal can and does happen, well known people have been given last warning and some declined entry from coming to often, doing border and visa runs.
As I and others said you can eventually be refused if going with a tourist visa or exempt if going to often, the IO will decide on the day like it or not it happens.