Your plants aren't getting enough moisture. Rubber plants will develop brown edges when moderately moisture stressed. Keep them moist. Any damaged leaves will have a shorter life span than unblemished leaves.

If you're watering while you can still detect moisture in the soil, especially in the top 3-4", you're likely over-watering. Use a 'tell' to 'tell' you when it's time to water. Also, plasmolysis (commonly: fertilizer burn) might be the underlying cause. If a plant is growing under very bright conditions and at the upper limits of what it's programmed to tolerate, (which they usually are, at greenhouse/nursery ops), moving them to a position with a reduced light load can cause fertilizer burn, even though the concentration of salts in the soil solution might not have increases. That the greenhouse fertilized when it potted you plant up increases the suspicion that fertilizer burn might at least be a component of the issue.

More about using a 'tell':

Over-watering
saps vitality and is one of the most common plant assassins, so
learning to avoid it is worth the small effort. Plants make and store
their own energy source – photosynthate - (sugar/glucose).
Functioning roots need energy to drive their metabolic processes, and
in order to get it, they use oxygen to burn (oxidize) their food.
From this, we can see that terrestrial plants need air (oxygen) in
the soil to drive root function. Many off-the-shelf soils hold too
much water and not enough air to support good root health, which is a
prerequisite to a healthy plant. Watering in small sips leads to a
build-up of dissolved solids (salts) in the soil, which limits a
plant's ability to absorb water – so watering in sips simply moves
us to the other horn of a dilemma. It creates another problem that
requires resolution. Better, would be to simply adopt a soil that
drains well enough to allow watering to beyond the saturation point,
so we're flushing the soil of accumulating dissolved solids whenever
we water; this, w/o the plant being forced to pay a tax in the form
of reduced vitality, due to prolong periods of soil saturation.
Sometimes, though, that's not a course we can immediately steer,
which makes controlling how often we water a very important factor.

In
many cases, we can judge whether or not a planting needs watering by
hefting the pot. This is especially true if the pot is made from
light material, like plastic, but doesn't work (as) well when the pot
is made from heavier material, like clay, or when the size/weight of
the pot precludes grabbing it with one hand to judge its weight and
gauge the need for water.

Fingers
stuck an inch or two into the soil work ok for shallow pots, but not
for deep pots. Deep pots might have 3 or more inches of soil that
feels totally dry, while the lower several inches of the soil is 100%
saturated. Obviously, the lack of oxygen in the root zone situation
can wreak havoc with root health and cause the loss of a very
notable measure of your plant's potential. Inexpensive watering
meters don't even measure moisture levels, they measure electrical
conductivity. Clean the tip and insert it into a cup of distilled
water and witness the fact it reads 'DRY'.

One
of the most reliable methods of checking a planting's need for water
is using a 'tell'. You can use a bamboo skewer in a pinch, but a
wooden dowel rod of about 5/16” (75-85mm) would work better. They
usually come 48” (120cm) long and can usually be cut in half and
serve as a pair. Sharpen all 4 ends in a pencil sharpener and
slightly blunt the tip so it's about the diameter of the head on a
straight pin. Push the wooden tell deep into the soil. Don't worry,
it won't harm the root system. If the plant is quite root-bound, you
might need to try several places until you find one where you can
push it all the way to the pot's bottom. Leave it a few seconds, then
withdraw it and inspect the tip for moisture. For most plantings,
withhold water until the tell comes out dry or nearly so. If you see
signs of wilting, adjust the interval between waterings so drought
stress isn't a recurring issue.

Al