What I suggest is this: open up your copy of the Traveller rules. I'll be quoting from Starter Traveller (it's the copy I have with me). Turn to the chapter on Trade and have a look at the Actual Value table (Charts & Tables, p22). For those of you without access to your rulebooks, I reproduce* it here:
When your PCs go to buy something, the referee rolls 2D and consults the table. If the PCs are willing to pay an extra 20% up front, the referee can add +1 to the roll. The result gives the extent to which the item purchased misses or exceeds stated expectations. This roll should not alter the price directly; that kind of negotiation should be role-played by the players with Admin, Bribery or Broker skill.
If the result is less than 100%, penalize the item by subtracting from its performance. Let's take the standard Air/raft (Rules, p 55) as an example. Our heroes want to buy one, and the referee rolls low, a 4. Some combination of factors must be reduced to 70% of listed capability.
This could be a 30% loss of top speed (84 kph), or an extra 30% mass (5.2 tons), or a 30% loss of usable cargo space; or any combination the referee can come up with. Unless the PCs ask good questions, they should not be aware of the vehicle's defects until after they've purchased it.
As a second example, the PCs (who passed on this substandard air/raft) decide to visit the ATV dealer, and pick a model. The referee rolls high this time, a 9. The tracked ATV (Rules, p 56) cruises at 48 kph, maxes at 96 kph and can off-road at 36 kph. Another model may have standard performance but only takes up 8 tons when shipping it.
The speed change can be a factor in escapes or chases - if the PC's vehicle is a bit faster than their pursuers, they stand a better chance of escaping.
This variation can be applied to more than just vehicles. Communicators can get better range or weigh more; weapons can be larger or more compact, or weigh more than 'standard'. To change a weapon's accuracy (the Range DMs) by +1 requires a 20% bonus on the table. (7+ to 8+ is a change of 16%, round up to 20%)
The referee may decide to raise the price by 5% for each 10% bonus in performance or let the PCs 'get lucky'. PCs who get a 'lemon' may want to attempt to upgrade the vehicle to fix the flaw. In any event, the vehicle/equipment is now more than just a note on the character sheet, it has some character of its own.
What do you think, fellow Traveller?
*This is fair use, tables and the like cannot be copyrighted.