Are you asking the seller to pay closing costs? If yes, then the seller needs to increase the price to include your closing costs. Example: If the seller is asking $500K for the home and your offer is $490K + $8,000. in seller assistance, this means you are actually paying $482,000. ($18,000. below the asking price). The seller will be very upset so to balance out the math, the seller will increase the price to $508,000. so the seller's bottom line is still $500K - not $482K.
If the $8,000. price increase is for something else, then I have no idea why the seller would increase the price.