Unfortunately, in Bahria, when site / land is developed, they change the natural landscape much, and sometimes it becomes difficult to judge which plot was in cutting and which was in filling. To overcome this, many people prefer to buy plots in such societies which only develop the land (like making roads, laying pipelines, etc.), but do not change the landscape, i.e. cutting / height remains as such, and ditches / trench, also remains as such. At least, potential buyer gets saved from scams.
YES! Definitely and 100%
Although not 100% true, but generally speaking, the plot which will be in filling, will have developed many small water channels, drainage paths, etc. when rainfall would have happened, and its surface would have become quite rough.
The plot which will be solid and in cutting, would be well compacted, rather naturally compacted, and might not develop such channels. Plots in filling might develop such channels due to improper compaction, differential compaction, etc. and which is man-made done too.
All the houses in Bahria will be clean, modern and earthquake resistant, as they deploy so much steel during construction, that structure is over strengthened, however, it may be noted that excessive steel in R.C.C. Structure is not good, as it changes the behaviour from ductile to brittle.