Pokemon Facebook pages are probably the lowest of the low. Without wanting to sound too much like this is the Elitist Fourum, you can comfortably write off a lot of what gets said on Facebook as pointless noise. With that being said, I want to address the main points of your claims.
Underlying everything must be an understanding that Pokemon cards have no inherent value. Their prices are determined by supply, demand, what people are willing to sell for, and what people are willing to pay. Because these are the only things that determine value of cards, and they can change very quickly, Pokemon cards do not have “market prices” as much as the 5000 sites that put sales into a line graph want you to believe.
“Market manipulation” (either up or down) doesn’t exist. Shill bidding is usually an isolated phenomenon and is likely done for purposes other than “manipulating” the market, like getting more money for a seller. There are some isolated incidents of coordinated and ongoing shill bidding on classes of cards designed to drive up prices, but with today’s tools these are quickly discovered. Many shortsighted people may try to “manipulate the market” by tricking the 5000 eBay affiliate price trackers into believing a card is selling higher or lower, thus altering the “market price.” The problem with this is that it is thwarted by people rubbing 1.5 to 2 neurons together and clicking “Sold Listings” on eBay and seeing that most real sales still remain within a reasonable, non-outlier range. As such, most market manipulation attempts by uninformed people dreadfully fail. Some shill bidding on a readily available modern Charizord or someone listing a bunch of cards for $1 and selling them to themselves are ripples in the lake of the market. Prices go up or down all the time, and this is not an inherent sign of manipulation.
Depending on the state of the market, buyers or sellers will have more power. If the market is hot, supply is low, and demand is high, sellers have more power. Why wouldn’t a seller laugh at someone who claims prices are “manipulated” if they have five other people standing in line willing to pay their asking price or very close to it? If the market changes and demand weakens, buyer power increases. Sellers might not have people lined up to buy their cards and instead are now competing with the 9 other sellers at the show for 2-3 buyers in total. This puts a downward pressure on prices and gives buyers power to pay less.
In all, it seems like you are conceptualizing power as price. If you pay more, you don’t have power. If you pay less, you have power. Remember that as a buyer you always have the power to set the price you pay for a card. If you don’t feel comfortable paying a certain price, you can simply not buy a card. You run the risk of others wanting the card more and increasing the price, but you always set your goals, priorities, and expenditures.