If I'm right, the sellers usually go by market rate, thus let's say valuation is at 350K and the market rate is at 370K, the seller will usually sell around that price, unless reno done very nicely and such, then MAYBE they might ask for slightly more. Of course, if the seller is asking for something wayyyyyy higher than the market rate, then its pretty hard to sell. which in the end, cause the seller to lose out since he/she wouldn't be able to sell it off at that high pricing.
Likewise, if the market rate is extremely low, even if the seller wants to sell it at valuation, no buyers might want.
But there are a number of sellers around whose asking price is just slightly higher than valuation and usually such flats are quickly snapped up. My friend got her flat for about 6K above valuation due to the last owners renovations which expand 1 of the rooms, so 2 rooms merge into 1, and its low floor, so maybe that is why no one wants it.