You did not include any information as to what scanners you had used, so it is hard to relate. But it is not true that most of them report alleged trojans. Some do, but it's a minority, and yes - in all cases it is false positive. It is not uncommon for many AVs to automatically flag software from an unknown publisher just in case. Whenever we are reported issues with any AV, we always notify them about false positive and request a wider analysis. In most cases it results in removing those flags, but some AVs have a very poor support that doesn't even care to answer. So, whenever you use those online scanners that include dozens of AVs, you should bear that in mind that not all of them are necessairly reliable. Also, those flags may reappear when the client gets updated and the signatures change.

To answer your title question: there is nothing wrong with the Tibiantis client. It has been used by thousands of players weekly for the past 4 years. If it does not speak to you, then I probably won't be able to convince you, so just don't use it if you are afraid.