Do they have to create a Uniregistry account to submit their offer? If so some people don't like creating accounts just to submit an offer as it may be a one time only purchase and they may have doubts their offer would be accepted anyway. "They probably want 50k" which might not be the case.
My reason for doing my own pages is basically I receive first/last name, email, phone, offer, ip address. No account sign up is needed and no future marketing to my leads from third party aftermarkets as once they create that account you just fed them another customer they can solicit/upsell/divert down the road. I'm a fan of building my own end user database without third party eyes on it.
Look at a Sedo parked page...
"Receive updates on this and similar domains.
Sign up and we will provide you with the best offers for"
Nothing more than a lead generator to their future email marketing list where if an end user fills that out now Sedo can email them a ton of domains in the same category. Maybe some are yours, maybe some are another domainers, maybe some are from their own portfolio. This is called your traffic possibly enabling someone else to profit or a traffic leak.
I believe third party aftermarkets shouldn't receive commission unless their distribution networks or their markets achieved a sale for ya Afternic, Sedo etc... as most leads come direct from the sales lander anyway so directing those to an aftermarket where leads come in anonymous doesn't help in negotiations and is basically just handing 15-30% of every sale away that you could have kept in house while building your own end user database. Build your own future not the companies that make 15, 20, 30% of every sale with the secret that their not out marketing your names your names are buried with millions at their markets with a generally horrible category structure that makes searching not so good and your own traffic brings in most of the leads anyway.
I'm fine with paying 20% when a distribution network lands a sale for me as this is the future putting domains in the natural path for end users at their normal registrar which doesn't require you to point your domains to them to make sales.
Domain Distribution Networks=Yes
Pointing Your Domains To A Market Where You Receive Anonymous Offers, Your Domains Are Burried, They Can Solicit Other Domainers Domains Or Their Own=Hell No
So in conclusion
I'll always do my own sales pages but I'm fine with paying a % for distribution networks that actually did some work or secured the distribution partnerships to achieve the sale.
https://www.afternic.com/domain-reseller-network etc...