Sight Unseen Offers

[Thomas Fortune]

For those of you who offer on properties sight unseen, what type of buffer do you give yourself for your reno budget? Every time I start to think to myself, "I've seen/done enough to feel good about offering sight unseen", I see something that changes my mind:

I looked at a property yesterday, expecting it to need a full cosmetic rehab and maybe a few mechanical items as well (roof, hvac,etc.). After viewing the property, i found some major foundation issue, a half completed addition that would likely need to be torn down (or started over from scratch), and a garage conversion that needed major improvement. - these items would likley triple the required reno budget.

How do you deal with this? Expect the absolute worst?