I agree with this--I think there has got to be a better way about it than with making the luthiers paying a fee to be accessible. If Luthiers wanted to pay for customer accessibility, then they would have budgeted money to get on google ads--there is a bigger audience, and if you only have $X to spend on advertising, then you are going to spend it on whatever reaches the most customers (imo it would be google ads)
I also don't think customers would want to pay either, as it's just a question--it'd be more economical to just keep googling luthiers and emailing them. The draw of the site would be for networking, and you don't really want to present either side with much of a hurdle.
I liked the idea of the 3rd party involved being asked for adspace purchasing--the parts makers/sellers, like
stew-mac, or maybe even graphtech and hipshot and similar businesses. My thoughts on that are that maybe having ads for parts might even be considered helpful, as they might help the customer better flesh out what they want on their instrument.
Maybe even GoogleAds might be a good idea, as they pick out certain keywords in the text to supply ads, and they should be relevant to the instrument design. Heck, maybe it'll hook up customers that way, and the luthier didn't even know it, but either way, if the payout is based on clickthrough, then the page would still bring in some money, even if it's not that much.