@Thomas S. "You do not waste time asking for credits you simply lower your offer to compensate for the repair costs."
Why is a lower offer inherently more desirable than an equivalent "higher price with credit offset" offer? For example, from a seller's perspective, getting $200k and providing $10k worth of repair credits associated with specific repairs has the same net impact to their bottom line as getting $190k; and, from a buyer's side, paying a financed $190k means you still have to cough up $10k cash immediately to execute repairs, whereas paying a financed $200k and getting $10k in credits means you get to amortize the upfront cost of repairs over the term of the loan and only needing to set aside $2k in additional cash immediately to offset the additional loan principle. Seems like it could be an easier pill to swallow on both sides to propose credits rather than putting down a straight up 'firm and final,' but let me know what I'm missing.
@Brendan L. Negotiation tactics are seller/market/property dependent. Why is the seller selling? Are they trying to get out from it quickly or can they take their time? Is the seller an investor themselves? Are they the type that would prefer to deal with things in writing or are in-person discussions more likely to be effective? I'd probably talk it over with your realtor/a mentor or possibly start a separate thread to source people's thoughts on this one.
Regarding the NPV & DCF calculations, the pages might be a bit complex but the idea is generally pretty simple - if I tell you I'll give you $100 a year from now or $x today, what would x need to be such that you were indifferent between the two offers?
More broadly, DCF helps you get an 'apples to apples' perspective on projects that have differently-sized cashflows at different times. For example, if you have one project with a large upfront investment and larger periodic payoffs and another project with a smaller upfront investment and smaller periodic payoffs, one answer to which project you should choose depends on the sum of the present values (the "x" in the $100 vs. $x comment above) of the cashflows of each of the projects - this present value is dependent on the length of time you're investing and your expected yearly return, as a discount rate (although there are a couple of different ways to select an appropriate discount rate, that piece can be researched).