If you are looking for foreclosures some banks will offer incentives that include part of the closing costs.

I think you have to look at each house individually to determine what you should offer and work with your lender and your agent to properly structure a deal.

You can always ask seller to pay closing cost. Just keep in mind that such a request is just as much a reduction in sales price as offering less than the house is listed for. Meaning, if you closing cost are $5000 and they pay those and house was listed at 100,000. Your offer is really for $95,000.

Point being, whenever you make such a request, remember its part of the offer as a whole, and you need to make sure the offer is one that's good for you, and that seller can live with.