Since you are curious about markers to answer you first question those are not Pied Markers, however:
Marker are not 100% accurate
Some het pieds have them some do not
Markers can be strong or not
This is an example of a strong markers
My advice
1# Never buy an het based on markers, buy an animal based on the fact that the animal is produced by a REPUTABLE breeder that guarantees the animal
2# When buying a second hand het ALWAYS make sure that you can actually verify that the animal is what he is sold as, ask to see the original paperwork and contact the original breeder. (Paperwork that come with a photography can help you and the original breeder confirming that the animal in question is indeed what he is sold as)
3#While many hets do not come with paperwork it's not a problem when
A# You buy it from the person who produced it and this breeder is REPUTABLE
B# The breeder who is selling a second het het is reputable and will stand behind the animal and guarantee it himself just like he would if HE produced it.
Again the key is REPUTABLE BREEDER
If it's non of the above just walk away.