How long do you research online to buy a product or service?

depends. sometimes I may sit on the idea for a few days

Depends on how complex & how costly the product is. It can take from few minutes to few months.

[b]Commonly my research goes like this.[/b]
1. Do I really need the product or services:
a) What value the product bring to me if I purchase
b) What I will lose if I don't purchase

2. What brand model/configuration/specifications I should purchase:
a) First I decide my budget.
b) What type of brand is right for this product. I may not require top brand for every product.
c) Finalize the brand / specification / configuration required depending on above research about brand & budget.

3. Finalise the perfect store / Website / marketplace to purchase the product.
a) Check what prices, schemes, discounts, warranties, accessories, offers are available.

4. Do the Purchase.

Depends on what I’m purchasing 😁

It could be a week or a month

Depends on the product.
Medical, Cars, Computers, extensively.
Shoes, I just pull the trigger.

Weeks or months, on and off. Depends on the thing.

Youtube reviews are the best ways to gauge a product's reliability