I've done the event board audits for a little over 2.5 years now. I currently have 5 that I visit. I visit them 3 days per week (T/W/SA). Over the 30 months I have been to 11 different hotels. Of the 6 that I no longer visit, there were 3 of them where I obtained little/no valuable information and I was told to not visit them anymore. Another location I'm not sure why they told me not to visit anymore, and 2 of the locations I was kicked out and told not to return.
The idea of people entering hotels and obtaining information on events being held is not new. The Knowland company has been sending their spies into hotels for decades. Also, individual hotels also send their sales teams into competing hotels with the goal to obtain the events happening in the competing hotels.
My advice would be to not give up. The amount in visit fees for 8 hotels is many thousands of dollars in the course of a year.
Take some time and study the hotels entrances/exits/hallways. For the 5 hotels on my route, I can either entirely or nearly entirely avoid ever being seen by the front desk staff by using alternate entrances/exits that avoid the main front entrance. Just yesterday I did all 5 of my visits and I never used any front entrance. I realize that this isn't always possible, but it's worth putting in a little extra time to drive/walk around the site and see the location of ALL entrances/exits.
If possible, you could also vary the time of day when you visit so as to not be seen by the same person(s). Again, I know that this isn't always possible.
I would also email Shannon at the MSC and ask if she has a general list of tips.
If you're visiting your 8 hotels each 3 times per week like I do, that's $240 per week, which $12K per year. Don't you dare give up that kind of money without putting in some time/effort to make it work! You'll love the 20th of each month when the payment hits your PayPal. I know I do. And hey, as I write this it's almost the 20th!
Good luck, I hope it works out for you.