Expressions of interest are different from for-sale threads, I guess.
In those cases, I assume the seller isn't sure if they want to part with it, it just depends if someone is interested and what they're prepared to pay.
I agree with Steve, if someone really WANTS to sell it, they'll list the price they want. If a price isn't listed, and someone IS interested, they'll PM the seller. I guess that's why it's called an expression of interest
