So, apart from the one unusual incident (which I think we've just about squeezed dry), there appears to be some sort of consensus: folkies do spend a lot of money, but on beer rather than other things.
I'd disagree, at least in terms of regular events I've been to - festivals might be different. These events have tended to pull in a small number of participants getting together from reasonable distances (may just be the nearest villages or towns but can be further) and driving is often involved and those that are driving are not drinking loads of beer.
Then there are those who will limit themselves to say a pint or two because they find more interferes with their singing and/or playing. Of the rest, there often people who wouldn't otherwise go to a pub and perhaps don't drink.
I've rarely seen the (at least participation) folk contingent do much in the way of contributing to a pubs turnover of drinks by their own consumption. While there are exceptions and some places do seem to do exceptionally well, I feel often it's the other customers' willingness to tolerate (or we hope enjoy) us or perhaps a spare room that's doing nothing but just needs a light turned on that makes it worth a landlord's while.
And yes, some landlords can see be big profits from folk and be dissapointed when this doesn't materialise. Usually one just gets "moved on" but I can even think of cases where landlords have moved in extra entertainment we couldn't cope with volume wise on the folk night:
Parade Llandudno - asked to miss a night for a rock group. Club moved to the London instead. Old Vaults Bangor - new landlord wanted the passing night club trade - blazing disco music - moved to Menai Bridge (couldn't find a place in Bangor at the time) Four Crosses Menai Bridge (a couple of years and a change of landlord) - Reggae night - moved back to Bangor (fairly recent "Irish Bar - O'Sheas - in a previous existance it had been the Kings, the venue used before a move to the Old Vaults was forced). Temple Bar Norwich - wide screen football - moved to the Nelson