In Yoreh Deah 240:25 says the following,
אִם הָאָב רוֹצֶה לְשָׁרֵת אֶת הַבֵּן, מֻתָּר לְקַבֵּל מִמֶּנּוּ אֶלָּא אִם כֵּן הָאָב בֶּן תּוֹרָה. תַּלְמִיד שֶׁרוֹצֶה לָלֶכֶת לְמָקוֹם אַחֵר, שֶׁהוּא בּוֹטֵחַ שֶׁיִּרְאֶה סִימַן בְּרָכָה בְּתַלְמוּדוֹ לִפְנֵי הָרַב שֶׁשָּׁם, וְאָבִיו מוֹחֶה בּוֹ לְפִי שֶׁדּוֹאֵג שֶׁבְּאוֹתָהּ הָעִיר הָעוֹבְדֵי כּוֹכָבִים מַעֲלִילִים, אֵינוֹ צָרִיךְ לִשְׁמֹעַ לְאָבִיו בָּזֶה.
If a father wishes to serve his son, it is permitted (for the son) to receive (the service) from him, except (in a case) when the father is a Ben-Torah. A student who wishes to go to another place (to learn Torah), so much so that he is certain that he sees it will be a sign of blessing in him learning in front of a Rabbi who is there, and his father protests him doing so because he is concerned that in that city there are non-Jews who are lawless, he (the son) does not need to listen to his father regarding this
The Rama comments on this halacha the following:
. הַגָּה: וְכֵן אִם הָאָב מוֹחֶה בַּבֵּן לִשָּׂא אֵיזוֹ אִשָּׁה שֶׁיַּחְפֹּץ בָּהּ, הַבֵּן אֵין צָרִיךְ לִשְׁמֹעַ אֶל הָאָב (מהרי''ק שֹׁרֶשׁ קס''ו)
And similarly, if a father protests against a son not to marry a certain woman that the son desires, he does not need to listen to the father (Maharik, Shoresh 166)
Based on the above information given, there is a practice among many involved in Shidduchim that the parents do research on their children's potential matches.
That being said, is it permitted for parents to turn down potential matches presented for their children without the children actually knowing about the idea in the first place? If yes, why? If not, is such a practice thus improper?
After some conversation with DanF in the comments it is to be noted that the Rama is stating such a halacha when the woman is already decided upon by the son.
The question that I have (as stated above) is different in that the son has is unaware of such an offer which was rejected by his father. Is the such a concept a "loophole" within the confines of the law? If so, is it within the spirit of the law?
(Please provide sources for answers)