From PackRat Recipe Wiki

Upstealing is when you take a low value card and make a series of steals to get a high value card, sort of like a PackRat version of Bigger and Better:

Generally this is a sign of boredom in the PackRat world, but there can be advantages to upstealing. The primary advantage is obtaining large value cards for a minimally priced card. Generally 100 point cards are in the range of 10-20 credits in any of the markets.