We can't trust them just yet because their is nothing at stake, I have seen so many teams do well during preseason and when the league title race start they start fumbling, besides by looking at the game you will see that this Bournemouth team is not playing with the same intensity as the are used to, because they knows that nothing is as stake, so they don't want to risk getting injured. I know that some football fan might think otherwise that Manchester united are picking up but as for me, they are still in Disney land because i wouldn't bet on them just yet, because I still don't trust them yet, let the season start first, after the first leg, before the reverse fixture will start, their performance then will determine if truly they are back to the Manchester united that can compete or not, but if Manchester united do not spend more money on incoming transfer more than they have already done, they might pays for it because the rest of other top sides are not playing.
At first we should see preseason matches as just games that aren't very serious, although i won't say Manchester United won't be doing well this season, if I should say that I think that will be too quick to judge when the season has not even started, there are still mistakes in the team but I believe it will be gradually solved, Bournemouth may not have given they strength we know them for, we have seen that but that's reason best known to them too, I don't know why I feel that Manchester United will not do bad this season as long as they are able to provide all their coach amorim need to make the team work perfectly again, betting on them is a personal decision, lets allow the season ro start first before we can conclude on anything.