In today's market, most appraisers tend to be on the conservative side. Very, very few are inclined to give an inflated value.
However, if you're in the market to buy a home, hold off on an appraisal until after you get a house under contract. An appraisal will cost about $300-$400 (roughly). So you really don't want to spend that until you have to.
Keep in mind, too, that an appraiser will look at the property's value from three standpoints: Market value, replacement value, and value based on income that could be generated from the property. That's fine, but really all you're interested in is the first one, market value. At this point--before you've even made an offer--an appraisal is overkill.
Instead, get yourself a buyer's agent--a Realtor representing you. The Realtor will be glad to run comps on any home you're considering at no charge. And because the agent is representing you, there's no incentive for the agent to inflate the value of any property you're considering.
When you make an offer, you'll include a financing contingency in your offer. And that, in effect, ties in with the appraisal. But the problem most folks are having today is that some homes aren't appraising for the contract price. You and the seller may agree on a price of, say, $400,000, but the appraisal might come back at $350,000. Almost never will an appraisal come back for more than the contract price.
Hope that helps.