Permissible and impermissible items of trade

Selling musical instruments

Q: I am in the business of selling sound equipment like speakers, mixers, and amplifiers. To remain competitive. I feel the need to offer a wider range of products, including musical instruments, despite knowing that music equipment may be considered haram. Given this, I have a few concerns: 

1. Is it permissible to sell musical instruments under these circumstances? 

2. If the income from selling such items is haraam, can I use that money to pay taxes? 

3. If selling musical instruments for profit is not permissible, would it be acceptable to sell them at cost price just to stay competitive in the market?

Selling an item to someone not knowing whether they will use it for something impermissible

Q: 

1. Would it be halal for me to sell gold to a cash for gold place because there is a high chance they will sell this gold to a refiner, scrap gold buyer or so on and they might use this gold to make gold jewellery for men etc.? 

2. What about selling grapes to a business that sell grape related products so the grapes I sell to them can be used to make their grape juice or it can be used for their wine etc. Will the income be haram? Because I’m unsure what they will use it for.

Selling animals for fighting

Q: For animals used in fighting such as roosters and dogs, their price depends on their fighting ability. If a rooster/dog is an excellent fighter, it would be expensive. So is it halaal to include the price of an animal's fighting ability in the overall price of the animal? Would the amount added to the price based on the fighting ability be halaal?

Purchasing a TV on interest

Q: I bought a TV with option of no cost emi of 3 months. After emi completion, Later I found out that it is not permissible and it involves interest as bank gives loan and charges interest and then I checked my statement and found out.

I usually buy items paying all amount but this happened first time that I had to take this option of no cost emi. From the day, I came to know I am feeling bad. Should I sell of my TV or keep it? If I sell I won't even get 50% of amount which I took. So I am in a dilema. What should I do in this case.