you've already figured out we don't know enough to answer your question well, but I'm going to assume you mean that you're a buyer and you want to negotiate that some of your closing costs be paid by the seller. In that case, your lender will have input because the type of loan you have will have different requirements for that. For example, FHA allows up to 6% today of the purchase price, that the seller can pay of the buyer's costs. However that is going to change with the upcoming guideline changes, and will be less. Some banks selling foreclosures will state that they are willing to pay "allowable" closing costs, so they limit what costs they're willing to pay for the buyer. Some banks/sellers also include a 3% seller contribution to buyer's closing costs in their advertising, as an incentive to buy.
Bottom line, it varies depending on the situation, your loan, and the seller in the transaction. That's when you lean on your Lender and your Realtor to advise you in that particular situation.
Then when you figure out what is allowable, you need to get the seller to agree. In this market where sellers have been hit so hard, it might be difficult to find sellers who have enough equity to pay a buyer's closing costs. Remember sellers have their own closing costs to pay, and they may not have enough or the interest to pay for your costs on top of theirs.
Again your Realtor and Lender can best advise you on what properties work best for you to get some costs paid, if you need them, and then, you negotiate.
Best to you,