What's the cover charge with the coupon?

I’ve made a couple of trips to this club over the last few months and this is a consolidated report of all those trips.

They have a free entrance pass coupon on the website. However, they still charge you $10 as an entertainment fee. I know about this through other posts on this forum and I have personally experienced this as well, previously. One of the trips on a Saturday evening, the lady at the front refused to honor the coupon saying that since they had a VIP dancer on stage later that evening and I’d have to pay the full $20 cover charge. I typically don’t like to haggle about such things at a strip club and so let it go.

I was out there again on a Thursday evening at around 8 PM. There were no VIP dancers on stage for that evening. This time the lady at the front says that I had to pay $15. I said, I thought that the entertainment fee was only $10 with the coupon. But she insisted that it was $15 and I had to pay it. Anyways, I paid it. I’m not sure if others have had a similar experience recently. I understand that $5 here and there is not a big deal, but I just feel that things have to be consistent and not random.