As an aspiring Shadchan I can tell you, you never give the specific reasons unless it is something that can be worked on or changed.
First of all, you ALWAYS start with “although they heard very nice thing about you”… then, for instance in OP case,
“after looking into it they felt it wasn’t a match. or
“after looking into it they feel your not her/his type.
Then when they ask what do you mean, you repeat
“They just felt it wasn’t a match.”
You might have to repeat this a few times till it sinks in,
Throwing in an “I guess it’s not Bashert, when it finally sinks in, then you say i’ll look into some other things.
Then you’re good to go.
Do not give any details cuz then they will make you nuts to elaborate which will always cause heartache for them & yourself.
Some people even make up stuff just to keep them quiet,
usually because they made the mistake of giving details.
The bottom line is they’re not interested. What difference
does it make of why, to the other side?
To go on a diet? That should be obvious to them.
To get a nose job? most people are well aware of their ultra jewish nose. To go back in time & get a counselor to save their
marriage? Common! Theres really no point and it’s usually a question of lashon hora, or embarrassing someone.