Various game shows and other contests have a rules clause like this within their official rules:
NO PURCHASE NECESSARY TO PARTICIPATE IN THIS PROMOTION. PURCHASE OF A TICKET WILL NOT IMPROVE YOUR ODDS OF (i) BEING SELECTED AS A CONTESTANT OR (ii) WINNING A PRIZE. FOR FREE METHOD OF ENTRY, PLEASE SEE REGISTRATION SECTION BELOW.
I know that clauses like this exists mostly due to US rules as well as state laws regarding lotteries/sweepstakes and the like. My question is on how this relates to traveling game shows as well as contests at conventions and other like events. Traveling game shows being the stage productions that are replications of the actual television game show (but unaired). Conventions being events like trade shows, theme conventions (anime, Star Trek, etc.). (I noticed that at these events there are always some kind of game show or similar event open to only those who are paid attendees to the convention.)
Using a real-life situation, while looking at an official rules sheet for Family Feud, they list a certain set of people who are both eligible to participate and ineligible. But never mention that buying a ticket counts. (In fact, according to their rules page, if a person without a ticket somehow walks in and registers for a chance to play, and is selected, that person would receive a complimentary ticket.)
The question is this: Does requiring a possible participant to buy a ticket (either to the event or convention in question), make such a contest/game illegal? For example: If the event is held at a trade show and the only way to enter said trade show is with a ticket, and at that event someone is holding a contest or the like and makes it only available for attendees with valid badges, does the fact that a compulsory badge/ticket purchase make this a violation of the law regarding lotteries/sweepstakes? (To answer a question: The intended audience for these shows would be those particularly in attendance of said conference/convention.)
I noticed a similar question had an answer here on the law exchange: What, if any, consequences exist in practice for "purchase required" sweepstakes & drawings?. The answer to that question is in the area of this however unlike that question, these are all games of skill and not chance. (ie. You would be asked a set of questions to make progress in the game and the more questions you get correct determines your prize.)