#1 Location, Location, Location: First off, get to know downtown, all the different districts, where is the nearest store (Ralphs) and other things that interest you, and deter you, about downtown LA. Then look at lofts in those areas.
#2 Get Ready: Make sure you qualify for the maximum you can afford, you may like a better unit that cost $10,000 more but someone else gets it because you weren't prepared. Once a loft is sold, it is gone. Sometimes these lofts are the only one at your price in the building, when you find something you like, grab it.
#3 Check them out: Look at the different lofts and don't forget the little things like guest parking, Is there going to be nearby construction soon, is the builder in bankruptcy. I would recommend going with a more established complex than a new one with issues. Remember, associations can be nightmares, so ask about that too.
#4 Be aggressive: When you see the property you want, and there is only one, try to find out if there is any negotiating room, if not, even offer over asking. Remember, there is only 1, and if other want it too, it always comes down to price. The person who is most aggressive get the property, the person who is not, loses.
As for an agent, Yes I have worked with a buyer in the area (he was a friend) and we looked at every building we could for about 6 months, then we wound up going back to the barker blocks as the area, price and location fulfilled his needs best. Sorry to say, I don't work with buyer's anymore (unless they're investors).
So find an agent that agrees with these points, who is aggressive, and willing to do all the research on each building. An agent that knows the area is helpful, but not always the hungriest, for me, I prefer the agent that works the hardest for you should get your business and referrals.