The appraisals on refis of investment property I've seen lately are definitely conservative with respect to prior months. If you are financing your investment (or refinancing) I suggest:
1) Meet the appraiser vs. having someone let them in. Ask if they are a "junior appraiser" or a fully licensed appraiser who can do investment appraisals.
2) Gingerly offer them comparables you personally have knowledge of. They may glance at them but they all take the input. Sometimes lenders are going down a list and the appraiser is someone out of the area and very unfamiliar with recent comps especially FSBO's.
3) Give them previous layouts from other appraisals conducted -- They're always grateful. If they're new, give them anything that will help.
4) Make sure they are not doing an investment property as an understudy. I don't know of a lender/underwriter that won't require the property be assessed by a fully certified appraiser.
5) If you're trying to get rid of PMI, a STATE certified licensed appraiser is required and there are hardly any of those in our state. And you are required to have 70% LTV to even apply for release of PMI on most investor loans.