If the house is for sale, more than likely people are snooping as you say with the EA. I would be happier someone snoop with me (the seller) than the EA. But again back to op question, the seller has a choice "game on" or "go to EA", so go for it op.
The house is only worth what someone is going to pay for it and if this is 50k less, this is the value. Money is not out there now and if the seller takes your opinion, could potentially not sell. You make out the seller to be a fool, easly intimidate and will get dodgy people.
Take a look at sites like 'sell it yourself' or similiar - these must be people shivering with intimidaion - complete nonsense!
there is a difference with someone calling an EA and making an appointment and someone juast knocking on your door unannounced. There is a chance for the EA to vett prospective viewers and even recognise time wasters. The EA will accompany the viewer who in turn can relax when viewing as they won't upset anyone with negative comments.
The house is only worth what someone will pay for it, but would you not rather exhaust every option to find that value? A take it or leave it offer on your doorstep is only going to favour the buyer.
Potentially of course the seller may not sell, but are you saying that any offer is better than no offer? When we deal in real terms and with issues like outstanding mortgages and the cost of the transaction then people do have to consider what they are willing to accept and whether or not they should engage a person that is experienced in the business of selling homes (your most expensive asset).
I didn't say that sellers were fools etc my point is that keeping a distance between the buyer and seller can leave room for a clear thought process devoid of in your face negotiation. When the EA acts as a buffer he can offer advice and just lay out the facts for consideration.
Certain characters are better at negotiations and can put spin on things and try and convince you to take an offer, do you want that in your kitchen?
As for dodgy people, well we all are aware that they are out there but if you organise a viewing through the EA you will have contact details etc for everyone that has entered your home, but if I kknock on your door and say I'm only in town for the next hour before I leave on business would you 'dance to my tune' even though you don't know who I am or how to contact me later?
As for the site you mention, I don't think it can be held up as a beacon for success.