In all honesty I don't believe we lie in our relationship beyond the occasional "white lies" most couples tell each other in order to avoid hurting one another's feelings from time to time.
Another instance would be to throw the person off when attempting to pull off a surprise.
In the past when I have dealt with liars I noted they often give short (evasive) answers to questions and try to change subject. In some instances they act "offended" that you asked the question or they imply you are paranoid or have "trust issues" (all the while not giving you an answer). After such a tactic many folks will avoid asking questions. However if one is a relationship where they feel they are unable to ask their mate anything then that's a sign that they're not in sync emotionally. You shouldn't be afraid to talk about anything!
The reality is "Asking questions doesn't necessarily mean one has (trust issues). However NOT answering their questions will cause trust issues! Honesty and transparency builds emotional security.
Having said that no one wants to get the third degree or feel like they're on "locked down" and have to account for every minute of their day. You also never want to project on another the sins of one of you exes. Deep down you have to examine the motive for (why) you're asking the question. If it is because you don't (trust) them then odds are there is nothing they can say that is going to change your mind long-term. If someone is not "trustworthy" then it's not worth being in a relationship with them.
Life is too short to be spending your leisure time playing private detective!