Masbooq starting his salaah while the imaam is in qa'dah or making salaam

Q: 

1. If the latecomer joins the Imam in the first or final tashahhud for even a moment, then does the latecomer finish his tashahhud before rising up (for either the third unit, or to complete his missed units)? If the Imam rises quite soon after the latecomer joins him in the first tashahhud, then is it a factor that the latecomer may be behind the Imam? 

2. A latecomer makes the opening takbeer while the Imam is in the first tashahhud. If the Imam begins to rise for the third unit while the latecomer is going down, what does the latecomer do? 

3. A latecomer makes the opening takbeer while the Imam is in his final tashahhud. If the Imam says the first Salam while the latecomer is going down to join him, what does the latecomer do?

Khiyaarur ruyat (the option of buying or returning an item) for defective items on online purchases

Q: I humbly request your guidance and a detailed, evidence-based response regarding the following scenario: 

Our business sells pharmaceutical machines and occasionally encounters defective units. When a unit is defective, we explicitly inform potential buyers of the defect, share photos of it, and sell the machine at a discounted price. Despite being made aware of the defect, some clients later refuse to pay, citing the defect as the cause. Additionally, we sell various other electronic items through our online store. 

In light of this, we request clarification on the following points: 

1. Seller’s Obligation to Accept Returns: If the buyer refuses to pay or wants to return the machine on the basis of a disclosed defect, is the seller Islamically obliged to accept the return and refund the buyer? 

2. Application of Khiyar-ur-Ruyah: Does khiyar-ur-ruyah (the option to inspect goods before finalizing a sale) apply to pharmaceutical machines sold with clearly disclosed defects? 

3. Khiyar-ur-Ruyah in Online Sales: Does khiyar-ur-ruyah generally extend to products purchased online, where the buyer may only see images rather than physically inspecting the item prior to purchase? 

Wudhu and fasting for a person who has a problem with bleeding gums

Q: I have a problem of bleeding gums. The bleeding occurs anytime during the day or night. Sometimes I am unaware of it and other times I spit and rinse my mouth when I get taste in my mouth. My questions are 

1. How do I maintain wudu in this state? This is causing me to perform wudu multiple times sometimes. 

2. How do I fast? I try my best to rinse my mouth continuously when I am awake to avoid swallowing. But I am worried about when I am asleep and don't know if I swallowed or not. 

3. If my fasts are becoming invalid what is the kaffarah I need to pay? Should I pay for all the previous Ramadans because I am not sure about when I started suffering from the bleeding gums problem.