Sounds like a case of an over enthusiast salesperson making extraordinary promises to boost that commission cheque to me.
I doubt very much his boss knows anything about it, especially on a property that you haven’t even bought yet and so the ability to do such a thing is yet unknown.
I have heard some BS from sales people, but this one has to be the best yet.
If you do sell your house and take your panels with you then you cannot reapply for the Feed In Tariff as your system would be deemed to be a second hand system and therefore not eligible. The incentive can be transferred to the new owners, making it a great incentive to buy your property (maybe at a higher price than without the installation).