This is very common with Buyer Fee Payable listings. The member wants to make sure you pay them a commission if you buy the business described in the listing. That being said, be very careful about the terms of the agreement. Make sure that you are not hiring the member to conduct an open-ended search for you (unless that is what you want). You should also not pay an up-front retainer. And lastly, you should not have to pay a commission if you buy a business other than the specific business described in the post.