Landing on any award is entirely random. Keep in mind that big-ticket items almost always have a lower inventory count vs. the smaller items, this explains why these are harder to earn. We have seen users land on a laptop on their first day and some have yet to land on something big after being on SellPro for an extended period.
The best tip we can give is to spread the use of your SellPoints, new awards are constantly being added on the PlayZone and using all your SellPoints at once is not the best strategy.
Another great tip is to look out for the promos and special events, these promos usually pack the PlayZone with extra awards within a short period of time, giving users a greater opportunity to land on something.