I dislike unwanted advice, particularly when discussing it would involve giving more information than I am willing to give.
Not the best example, but one that springs to mind is yesterday I mentioned that I need a new phone. I have fairly complicated (but boring) needs when it comes to phones, but a friend insisted on telling me what I need - she has XYZ, and I must be mad to get an iPhone when there are so many cheaper ones available, and there is no need for unlimited data, as 65GB is more than enough for anyone. In fact, I do need unlimited, and I also need an iPhone as I connect my MacBook and iPad for working. I also need a lot of storage for various reasons. I didn't want to go into all that, but she clearly thought I was either too dim to follow her instructions or just profligate. I'm neither - It's just that I know what I want and don't need unsolicited advice about it.
Another friend can't resist pointing out various ways of getting the best deal on things to do with house maintenance. You'd think she was the only person to have ever had any work done, and that everyone's priorities are the same as hers. One difference is that her husband is younger than mine, and happy to carry out hard labour, and for various reasons I don't want mine doing that. None of her business, but when she's in full flight, there is no way to sidestep it, as she offers to phone people who live near me to see if the man who did Carole's driveway in 2001 is still available, or sort out an appointment for a quote. She also believes that because she has no boundaries when it comes to talking about personal matters, I should be happy to tell her anything she's curious about. Not my style, though.
I think that if someone says 'I am looking into doing X, and wondered if you had any experience/advice/thoughts' then fine - opine away. But without an invitation it's best to keep your thoughts to yourself, or offer a brief 'So and so has a sale on' sort of comment, and leave it at that. I might sometimes say (usually to my children) 'do you want suggestions, or are you just chatting?' which saves any misunderstanding.