Conversations with a customer.

Had an interesting conversation awhile back with a customer who had bought two lots from me.

one of the lots was a Scott #507, strip of three showing center lines at the top and right edges and J78 plate block of six that was canceled but still had full original gum - see images below.

It's almost unnoticeable but there is a faint diagonal streaking of black color from the top right to the bottom left. I had no idea what it was when I posted the stamp and must have described it in a way that sounded like a it was a fault. I've seen this effect only one other time and it was on a #507 single.

This plate block of six is obviously cancelled but still has it's full original gum on the back. It was another case of "what the devil is this all about?".

The customer sent back to me some very interesting information about these two examples (note: I did not correct the text, this is exactly as it was written) -

thank you ...i am a very advanced collector but i like weird stuff
....the 507 strip is a GREAT position piece ...i love the double inter
pane position line ...i know straight edge stamps and stamps with
position lines are very out of style but i like them in spite of that
...as to the used plate block  of J78.... to resolve the mystery of why
it is canceled yet has original gum ...it really wasn't postally used
....it is a RECEIPT USAGE.....when customers brought parcels to the
post office ( or for other large transactions) the postmaster would
cancel blocks or sheets of stamps and give them to the customers as a
receipt .no computers or printers back than......most often blocks or
sheets of the postage due stamps were used for  this ......post office
regulations required that the receipt stamps be affixed to something
but this rule was most often ignored ...that is why used sheets and
used large blocks and used plate blocks of the postage due stamps are
not that rare and why most have full or partial original gum ( just
like a pre cancelled block..)....some( like j 78) are rarer than others
or are worth considerable money as mint plate blocks and these do have
philatelic value .i have a full used sheet of J  78 and it is very
valuable.used plate blocks of J 78 generally sell for about 50 dollars
this is my fifth or sixth such piece......receipt usages on blocks or
sheets of regular issue=2
0stamps can be very rare and do have
considerable value ...i happen to own the only  used sheet of 573 in
the world and it was  probably a receipt usage but is worth a small
fortune ...look forward  to my new pieces be well ...

hi mike i am in receipt of the lots...i appreciate your notes
...obviously i knew i was bidding on a plate block of J78.....J 78 is a
flat plate plate block of 6 and a 5 dollar stamp ...J79 is a rotary
plate block of 4 and a 1/2 cent stamp.....b.t.w. i bought a collection
for next to nothing years ago that has round the clock used plate
blocks of the entire series beginning with J 79 for every duralnd plate
number ...it is really a remarkable collection and must have taken some
nerd a lifetime to accumulate....as to the strip of 507 THERE IS
NOTHING WRONG WITH IT ......it has some color run caused by excess use
of plate wash during production ....if you look closely at a lot of
stamps the paper in the  white margins  has a slight tinge of the color
of the stamp ...on black stamps this phenomenon is more noticable...but
look closely at the columbians...a lot of the darker colored stamps
...especially 234 ( a brown stamp) exhibit slight plate wash
color....it is natural and not even a callable fault....be well and
relax....

If anyone has anything else to add to this and would like to share I'd be happy to post it for you.