I think the general consensus is that the Electronic Gottlieb games are a bit of an "acquired taste" shall we say, and therefore cheaper than their Bally / Williams Peers.
@JMP is far more knowledgeable than me and has a fantastic collection of these machines.
The seller is Peter Hardman who had a fall out on this forum a while ago - IIRC, he had bought cheap off here and then selling outside the community at higher price- that didnt go down well. he seems to sell motorbikes and pinball machines. I'd comment, from me keeping an eye on his machines for sale, that they are a little over priced, so if I was after a machine from him, I'd be aiming to get a discount.