Sellers can get a fair price for their stuff even under the current scenario, if they do adequate research and price them accordingly. We have a good thread on "How much to sell stuff for" for the same reason.
1. When it is put under auction, people who are not interested can also easily jack up the prices by bidding just for fun. A genuine buyer with a real need will end up paying more than what it is worth, just because he direly needed it, and some troll in the market section bid for fun.
2. Also, I'm sure people will bid in increments of Re.1 and claim that he being the highest bidder, deserves the product. Now, this can be overcome by making a rule that the minimum bid increment should be Rs.X, but, do we need all this complication?
3. Both seller and buyer, under the current system, at least have a minimal amount of interaction BEFORE the deal to establish some trust. Both also do their homework, by checking out the current market scenario, and then decide on what price to tag something for or pay something for. I don't think that such stuff will happen, once auctions are in place. Remember, TE is a online community, with market section meant to just offload excess or unused stuff, and not to gain profits. This entire mindset will change, and people will tend to consider TE as a site to make profits with their stuff, without the hassles and troubles associated with ebay.