The garden centre would say that, wouldn't they?!
They are selling them as houseplants.
There is no such thing as a 'bonsai'.
The literal translation of bonsai into English means 'tree in a pot'. There is no such thing as a species of miniature bonsai tree and you can't grow from so-called 'bonsai seeds' either. They are just ordinary tree seeds, and won't grow into a bonsai by themselves.
And trees and shrubs grow where? Outdoors. Some come from warm climates and need winter protection, others can live happily outdoors all year round. In fact they need the changing seasons in order to remain healthy.
The reason yours is constantly dry is that it is planted in Chinese mud, which is fine for growing in China (and where they grow them in the millions for the UK market), but not for our climate or indoors. Once it dries out it is really difficult to get evenly wet again. You pour water on, and it runs straight off and doesn't soak in.
For an indoors species look for a ficus ginseng (they sell these in Ikea quite often) or ficus retusa.
There are others that can be kept indoors, but they are tricky tropical plants and need a tropical climate to grow well. So unless you can provide a jungle environment in your living room, you won't have much luck.
To have a go at starting your own outdoor one, buy a small cotoneaster from a garden centre, and prune it into a pleasing shape. The book I mentioned goes into detail.