Price Difference - Landfill/Bharai Plots

Four questions on landfill (bharai) plots:

  1. How important is soil test before buying a plot?

  2. What are the disadvantages of buying a plot which is in landfill (bharai) area?

  3. By what percentage should the price of landfill plot be lower than solid ground plot? I mean 20% lower than solid plot or even more difference?

  4. Should someone buy landfill plot at lower price?