The seller may 1) add it to their sales price or the seller may 2) accept your offer price and deduct it from their "net" proceeds.
Let's use the exmple of of a flat number such as $3,000 for your seller's assist and $100,000 for the price of the property.
$100,000 Listing Price + $3,000 Seller's Assist =
$103,000 as the price you will pay for the property
$100,000 is the "net " number to the seller
$100,000 Listing Price - $3,000 Sellers Assist =
$100,000 as the price you pay for the property
$97,000 is the "net" to the seller
In Philadelphia your closing costs will be about 5%-6% of the sales price so let's use 5% to see what the difference between the two scenatios would cost you.
$103,000 x 5% = $5,150
$100,000 x 5% = $5,000
Total difference is $150
The difference on a mortgage payment for a $100,000 home compared to a $103,000 is only $15 bucks a month. I am guessing on that.
Off subject, it is Philadelphia Beer Week and I see youare from Downingtown. We had Victory Brewing Company visit or neighborhood to host a Beer tasting at the Foodery last night. it has been years but I visited Downingtown. But I did visit one time to check out the Victory Restaurant. I had a great time there.
Hope this helps