The job of the appraiser is to write down a number as large as or larger than the amount to be financed. They know this and they know the number in advance. What they do is not rigorous.
They won't write down a completely insane number. They're a first level filter not a fine detailed filter. "I'm willing to go on record that I found three recent sales in the neighborhood for about $whatever" where whatever is reasonably near what you're financing. One need only go a few miles to find houses a tenth the cost or ten times the cost. If your neighbors house sells for $X and you want a loan for $X they're not going to sweat it, if you are trying for a loan of $X times ten its going to be difficult.
I paid a couple hundred bucks for an ex-general contractor with a thick binder to inspect my house for hours, looking inside the furnace heat exchanger and testing every wall outlet and inspecting the plumbing and roof inside and out and insulation and foundation and everything. That is a detailed analysis of what you're likely to spend on maintenance and upgrades over the next ten years. Its probably more useful than an appraisal but it takes a lot more time and money.
You seem to think these industry controls are effective. Maybe they prevent an appraisal from being, say, 10x higher than the recent sale prices on either side, but they don't prevent the equally bad event of a series of 10 sales on the same block each being 10% higher than the previous. Every one of those houses in Las Vegas that turned out to be worthless in 2007 was appraised for at least the sale price the year before. The appraisers in those cases didn't do a damn thing, for example they didn't come out to the house and write down "this neighborhood is in a desert with no access to water where the unemployment rate is 20% and the employed people make minimum wage therefore this cannot be a neighborhood of $850000 houses." They just said "the last house sold for $800000 and this market seems pretty hot so $850000 okey dokey."
Certainly you can influence the appraiser, but the way you state it is nonsense. Their job is also to provide feedback to the buyer, they won't just pull any number you like out of a hat.
What incentive does the lender have? The involved parties are the seller, the buyer, their agents, and the originator of the loan. All of these people are working to close the deal at the negotiated price. The originator of the loan will hold the loan for somewhere between 72 hours and 30 days, so they don't care.
Of course they care; any money they give you over the value of the home is unsecured! They're not going to lend you e.g. 20k @ 3.5% with no collateral. C'mon.
I paid a couple hundred bucks for an ex-general contractor with a thick binder to inspect my house for hours, looking inside the furnace heat exchanger and testing every wall outlet and inspecting the plumbing and roof inside and out and insulation and foundation and everything. That is a detailed analysis of what you're likely to spend on maintenance and upgrades over the next ten years. Its probably more useful than an appraisal but it takes a lot more time and money.