A lot of really good advice in this thread. I love to download people's builds from the Gallery, but I've had to tweak and rearrange a few restaurants to get them to work properly. Some of my observations are:
Using MOO too much does seem to cause a lot of small issues so I'd recommend to use it sparingly if you intend for the build to be playable.
I know that there are some builders out there who build for the art and creativity more than functionality, and that's perfectly okay. But it would be helpful if there was a tag for those types, like #nonfunctional or #justforshow or something like that, or at the very least, #NOTplaytested. This would give fair warning to someone looking for a working lot to plop down into their game.
I've noticed also that there are many "flexible" builds where the builder wanted the player to be able to use it as they choose, so they include all objects for bars, cafes, restaurants and night clubs. I find that, in the end, these end up causing more headache than convenience and end up with too much wasted clutter bogging down the lot as well as unused space. Sims will end up routing around for random things and not behaving as they're supposed to. So it's really best to keep it simpler and focused and let the player renovate themselves if they wish.
Finally, there are many restaurant lots that include a "liveable" space upstairs for the owner. While this is convenient for those who like to own restaurants and use that gameplay, these lots aren't the best for players who just want their Sims to visit and go dining. So this advice is probably more for the players. If you must download one of these lots to use, make sure you lock the doors to the residential section (or remove the doors altogether) so your Sims don't try to wander up there. You might even want to delete computers, TVs and stereos, as previously suggested, just in case Sims still get distracted by them.
I know there are players who say restaurants are very buggy, but I have several good working restaurants in my own game (some I've had to alter) so it's possible that many issues are caused by things mentioned in this thread. I'd suggest to try out a simple, spacious, non-MOO, focused restaurant (maybe one by Maxis) and see if it works properly. If it does, then you'll know that you just need to do some tweaking in the other restaurants in your game, or get new ones. If it doesn't, then you most likely have a bug.
