It is impossible in the examples you mentioned for one partner to sell their shares for a higher or lower price;
I can assure you it is completely permissible to sell one's share anyway you wish. There is no Shar'i complication with it.
just like you can not sell half of a car, you can not sell half of a house.
No one is selling half the car. We are selling shares in it. Up until now you had no issue with diminishing musharakah. The whole premise of the diminishing musharakah is that the shares of one's ownership decrease when one sells them. So that is definitely akin to selling portion of the house. The only difference is that when you own 50% of the house, it does not mean that you own the east side or the west side of the house. It means that the item [in this case car or house] is musha' i.e. multiple people have right in every single particle of the item.
This concept is not an advance concept in Islamic Jurisprudence.
So, therefore, both partners' interests are being vended for the same price.
Since you are mistaken on the above concept, your conclusion here is fallacious.
However, under the Islamic financing that exists today, despite the partners selling their shares for the same price, the proceeds are not divided accordingly.
If, in a financing model the price for the share is pre-stipulated according to whichever benchmark, then that is a mutually arranged price. However, since in a diminishing musharakah, sale/transaction of this month's batch of shares to the client is INDEPENDANT from the transaction which will be happening next month, the stipulation of price of the share is merely an ijaab (offer). The ijaab will either be from the client's side to purchase the next shares at particular pricing OR from bank's side to sell them at a particular pricing. Merely ijaab being found does not impose the buyer to make qubool of that pricing, so technically every month when the client buys further shares of the house, the client as well as the bank has full autonomy to negotiate on a new pricing.
So, quite frankly, your approach to the whole issue desires a lot of review.
If the price is high, one party receives the lions' share, while if the price is low, the other party is unfairly rewarded. In either instance, one partner can never receive less than his original "investment" while the other can.
There is no investment brother. There is a commodity and a person is buying a share in it. You are completely confusing the mode of Shirkah here. This is "Shirkatul Milk" and NOT "Shirkatul Aqd".
This is not permissible in Islam, no matter how you try to spin it. The hadith clearly say that risk and reward must be shared, which is NOT the case here.
Could you please post the hadeeth with reference that a shareek in an item may not sell his share lower than the the original pricing. Here I give you the hadeeth when mentions the concept I had mentioned. When a shareek has to sell his share, then that must be presented to the other partner first.
صحيح البخاري (3/ 79)
2213 - حدثني محمود، حدثنا عبد الرزاق، أخبرنا معمر، عن الزهري، عن أبي سلمة، عن جابر رضي الله عنه: «جعل رسول الله صلى الله عليه وسلم الشفعة في كل مال لم يقسم، فإذا وقعت الحدود، وصرفت الطرق، فلا شفعة»
The shuf'a is the right to the share before it is sold in open market. Mustafa al Bughaa mentions in explanation :
(الشفعة) من شفعت الشيء إذا ضممته إلى غيره سميت بذلك لما فيها من ضم نصيب إلى نصيب وهي أن يبيع أحد الشركاء في دار أو أرض نصيبه لغير الشركاء فللشركاء أخذ هذا النصيب بمقدار ما باعه.
i.e The partner will be presented the share in value of the amount for which the other partner wants to sell in the open market. The shareek will either pay that listed price, or will relinquish his right to purchase.
I feel since you are still looking at this from the Shirkatul Aqd point of view, your conclusions mismatch here.[/quote][/quote]