In summary, the manipulator will first pump up the floor price by sweeping the floors, which will cause farmers to revise their bids to max farming #blur. Then the manipulator simply dumps the bags on the farmers.
What the #Blur farmers are doing is providing liquidity to the bid side of the "book." Providing single-side (especially bid-side) liquidity makes the farmers susceptible to toxic order flow produced by manipulators.
On a side note, "toxic order flow" is a term used in market-making to describe orders that have a detrimental effect on the market, typically due to their large size. These order flows are made by informed traders, in this case, the manipulator with the plan to dump on you.
How to mitigate the risk of farming #Blur? You must carefully monitor orders and adjust their strategies to minimize exposure to toxic order flow.
For example, you need to monitor the executed trades and might withdraw your bids if you can identify floor sweeps that significantly pump the price.
Second, the mainpulator can pump the price because of the thin liquidity on the ask-side liquidity (meaning few people selling). So collections with a lot of active listings is less susceptible to manipulation, as it would require much more capital to pump the price.
Providing liquidity could be a very delicate PVP process, and it's easy to fall victim of a "highly profitable trading strategy" like @DanielVerilog mentioned.