Not really a common issue indoors but can be if your bonsai go out to catch some sun.
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<p><a href="https://commons.wikimedia.org/wiki/File:Grapevinesnail_01.jpg#/media/File:Grapevinesnail_01.jpg"><img src="https://upload.wikimedia.org/wikipedia/commons/6/69/Grapevinesnail_01.jpg" alt="Grapevinesnail 01.jpg"></a><br>By <a href="https://de.wikipedia.org/wiki/User:Heliodor" class="extiw" title="de:User:Heliodor">Jürgen Schoner</a> - Originally uploaded on <a href="https://de.wikipedia.org/wiki/Main_Page" class="extiw" title="de:Main Page">the German Wikipedia</a> as "Weinbergschnecke 01.jpg". Own work of <a href="https://de.wikipedia.org/wiki/User:Heliodor" class="extiw" title="de:User:Heliodor">Jürgen Schoner</a>., <a href="http://creativecommons.org/licenses/by-sa/3.0/" title="Creative Commons Attribution-Share Alike 3.0">CC BY-SA 3.0</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=201455">Link</a></p>

I have however had problems with very small snails that seem to have hitched a ride in on the moss that is sometimes used.

Damage to leaves and a slime trail are usually the giveaway for this problem.

Mostly they can simply be removed manually, but since they can do a lot of damage in  a single evening some enthusiasts like to be a bit more cautious. Keeping plants elevated of the ground is a simple yet effectively good start.

Bait can be put out but caution should be used with this where there are pets and children that frequent the area.

Just as a little aside:

Snails are so successful and diverse that they have spread from water to land and back again a number of times. As a result you can find land snails with gills and aquatic snails with lungs, even in the sea.