If the property appraises for less then your original offer then the best thing to do is write up an addendum stating just that to the seller through your agent and renegotiate the price assuming that the lender will still give you the loan first of course and they will let you know.If it goes down then that should save you money anyways and if they won't give you the loan then it wasn't meant to be.

I agree with both answers on many levels. My question to you is who is your REALTOR? If you are wanting to purchase a bank owned home you need an agent that can work through these types of homes. That REALTOR should have some type of foreclosed bank owned property experience. Becareful, remember there are little or no disclosures with these listings.

An exterior driveby value is usually always higher than an interior appraisal. the exterior doesnt show interior condition, age of the furnace, electric, plumbing and such. condition plays a huge part of value. from the outside it may look tidyt but from the inside you can see the homes true value. so yes they often go down when someone gets inside to do a real appraisal.

Absolutely!
The appraisals can vary. An exterior appraisal by definition only judes the exterior of THAT home in THAT neighborhood. The price opinion must asume that the property is in average condition.
If the value drops below $180K, then the mortgage may not go through.
By the same token, you may not want the house at $180,000 if the appraisers opinion of that property is less than your purchase price.
Would you really want to BUY at an above market price?
If it fails to appraise, you may wish to suggest to the seller that since you cannot obtain financing at $180,000, that you need to be released from the deal with return of your earnest money or you need to renegotiate the purchase price to be in line with the appraisal.