Wine samples are one of the best ways to demonstrate the character of a wine. As a rep, we take a bag full of different wines to show our customers. It is assumed that every day, we will bring a fresh set of samples, and the wines will show very much as they would if you opened it and drank the entire bottle in one or 2 evenings. In many cases, in an effort to save money, either from the distributor, or the sales rep (preserving their sample budget), the rep takes wines out a second day. This is one of the absolute worst things a rep can do.
Day 2 wine samples are very different than day 2 wine on your counter. Every time you open the bottle, pour a splash, you are decanting the wine. With that fresh oxygen in your bottle, you now take that wine, shove it in a bag, swing it for a walk to the car, stick it in the trunk, and then speed off to the next account. Silently, in your trunk, the wine is continuing to react to the new oxygen and agitation. A half dozen accounts later, and you have effectively aged this wine the same as spending 3 days of being open on your counter. Take that same wine out day 2, you are a) not really going to sell anything based on the tasting profile b) showing a wine that isn't acting like itself, doing a HUGE disservice to the brand and the people that made that wine. Many accounts won't really comment about a wine on the second day because they may not know how the wine is supposed to taste, they will just be underwhelmed and pass on the wine and the brand.
There are of course some exceptions. You can't kill Amarone or Ripassa. Many high alcohol, high acid wines do well on day 2. Warm weather wine that doesn't see much oak does ok, and the best for day 2 is without a doubt, great Mosel Riesling (ironic since it is such a delicate and seemingly sensitive wine). This is a limited list, and most aren't really optimal on day 2 (except Mosel Riesling).
If you have concerns about stretching samples, pull 2 bottles or squeeze in more appointments. You can always contact the supplier and ask for a free sample bottle, they will always prefer to pay for a bottle vs you showing a bad day 2 version of their wine. At the end of the day, it's a judgement call, and it's your judgement call.