The choice of selling agent would have no impact on whether I bought a place; once the offer is agreed, and they’re legally obliged to put all offers to the vendor, it’s all down to solicitors, so the fact that you don’t like the selling agent means very little.
And they can push their services as much as they like, if you don’t want them then politely decline.
Unfortunately the world of estate agents doesn’t quite work like this if the estate agent is based on commission and gets both money from the sale and the mortgages etc. If they have a client who is willing to use said facilities they will push that buyer towards the seller a lot more than you or so I’ve experienced
We’ve had exactly this happen, we lost the house based on me saying no to their mortgage advice. How do I know? I spoke to the vendor, she told me all the lies the estate agent told and what he’d said about us and how much he was pushing one particular buyer who was using all their services, we were only able to proceed with the house when the vendor told him she was pulling the sale (him losing both commissions) and getting her solicitors involved for dodgy practice, as soon as this happened he backed off and suddenly let us sort things out.
I know its only one case but it happens.