Peace proposals unaccompanied by a sworn covenant indicate a plot.
In a military arena where both sides agree to a tacit code, then both will likely follow that code, but nothing else. Where the code says that a sworn covenant will be followed, but anything else is allowed, then only the covenant can be believed.
Understand the codes that your enemy will follow, including of honor and dishonor. If the code is ‘All’s fair in love and war’ then do not even believe a covenant.
One thing that may happen is where an enemy has different codes to you, but acts as if they follow the same codes, so deceiving you.