We found that shopping with all the new found loot at the end of an adventure/session can be very tedious - having to roll for rarity, etc. so we use the following house rule:
each market or planet has rarity value
each player can purchase items of that rarity or less without problems (max 2-3 of each item type) - just shopping around the market
if item is restricted or higher rarity value, then each player can roll for 1 such item per person per market per session.
this then keeps tedious rarity rolls to a minimum, and also restricts the amount of restricted items the party is using. Trader, I'm looking at you :-)
of course if the shopping trip is part of the adventure plot, then GM can insist on rolls as normal.
Be interested if anyone else has a similar house rule, to keep the fun rolling along.