On Wednesday, April 17, 2019 at 1:08:53 AM UTC-7, wrote:

Originally it was N797SD, sn 107T503LSA. Currently carrying a different N number and serial number...

Searching the FAA database on the N-number in the ad, I see that it reports the exact serial number you cite. So that record is straight.

As for the ad reporting the serial number as 177, that could be a simple typo on 107, which is likely the part of the serial number that represents the aircraft's position in the production sequence.

--Bob K.