There was a question about trustable and it was mentioned that it started to be used more often only recently. Thus, I am a bit worried about its usage in IELTS Academic writing.
Like an example from Cambridge Dictionary:
a trustable source
The question: Can I use trustable in IELTS Academic writing?
Merriam-Webster does define "trustable" as an extant word (https://www.merriam-webster.com/thesaurus/trustable), but still, it would certainly seem odd to many people and hence other words such as "reliable", "trustworthy" and "bankable" are much more preferable.
Currently there is a tendency to use adjectives with 'able'-ending both in speaking and writing. Words such as DOABLE, WORKABLE, COACHABLE, MANAGEABLE are commonplace. That being said, I don't feel that trustable is in this shortlist yet. So, if I were you I would stick to RELIABLE, CREDIBLE instead.
As for common mistakes and words choice for IELTS, I would recommend Facebook page @tuto.ielts. It features typical writing mistakes, so it can be useful.
Disclosure: I make regular contributions to that page which link I provided so I would be happy to see you there.
