I will only do an as-is deal. If something is way off then I ask the Seller for price concessions, but at the end of the day if the deal will fall through because of it you need to check if it's worth absorbing or if you're ready to walk away over it. I don't want them to fix stuff with bubble gum and bailing wire, and then I have to fix it again 3 months after takeover.
I walked away on a Park that had oil drums in the creek that the Seller didn't disclose, another that needed complete water and sewer replumbing, etc. These are big issues and unless the Seller will work with you on them then walk away.
If you're talking about having to trim more trees, or patch more asphalt than expected, then you can probably spread those costs out and eat them.
The MHU Due Diligence Manual details the process if you don't have it already.