I can’t manage this dog

[Atwitzend123]

Hoping for ideas/ inspiration as this is an issue I have to resolve.
Too many details might be outing but briefly I am meant to be looking after a terrier dog due to its owner’s very difficult circumstances and I am failing.
I love dogs. I have had experience of many breeds over my lifetime. I am no spring chicken.
I had met the dog several times outside prior to visiting to walk him. I think part of the problem is that I can never be there when the owners are present.
The dog is not generally friendly. He was nervous when I went in for the first time a couple of weeks ago. I was friendly, chatty, but gave him space and have continued to do this. He now lets me near him, but not normally close enough to touch.
It occurred to me that maybe he perceived my reticence in approaching him as me being nervous of him, which might have made him worse.
Today I walked in as normal and slowly but confidently walked up to him, talking all the time and put my hand out to stroke him. He tried to bite me. He wasn’t cornered. He could easily have moved away, so I can only assume he chose to bite.
I didn’t react except to move my hand back and firmly tell him no.
I made no further approach but sat there for over an hour, occasionally talking to him, but he wouldn’t come near me, and won’t even go out in the garden.
I don’t know what to do next. I am trying to help and don’t feel that I can ask anything of his owners at this difficult time.
Does anyone have any suggestions?

He's scared of you.
I would recommend watching 'Dogs Behaving Very Badly' - there are episodes on YouTube. Graham, the presenter and dog whisperer, has some very quick solutions to the kind of behaviour the terrier is displaying.
I hope you get things sorted, you poor things, both you and the dog.

To be fair to the poor dog, my dogs are very friendly but they wouldn’t react well to someone walking into the house when I’m not there, particularly if I’d never been there to show them that person is “safe”.
Is he food oriented? If he is, take something super tasty that he would perceive as high value (chicken/cheese etc. check with owner first that he has no food intolerance) Sit down and ignore him, don’t look at him, but throw pieces of food in front of him. Over time throw the food further away, so he gets nearer to you. Eventually, he should associate you with nice things. That has worked for me when I’ve adopted/fostered very frightened or aggressive dogs.

I do feel sorry for the poor dog. His world has been turned upside down by a relationship break up and a serious health issue which means his owners aren’t there with him nearly as much as he has been used to.
Unfortunately he is not at all food orientated. His owners give him the best fresh foods and this is often uneaten in his bowl.
I have sat in the house for over an hour at a time, but I just don’t seem to be making any progress. I’ve tried all sorts of toys, and both chatting to him and ignoring him.
He is said to be ok with other dogs but my dog isn’t always friendly, so I don’t want to take her with me in case it causes further problems.

Thank you. I will look that up. I hate to think that the poor dog is scared of me. I have tried to give him space and am always friendly. I do realise that he has been out in an awful position though.

I don't recommend Dogs Behaving Badly, the training methods aren't good and you don't want to be using harsher methods on an ready anxious dog.

I agree with the Buildingthefuture's suggestion of throwing super yummy treats for him, but not looking at him (sitting on the sofa, side on to be less scary). Take it back a level, you approaching him today was obviously a step too far for him.

Urgh not food motivated makes it harder. Sorry if I'm stating the obvious - but have you tried super high value smelly food? Cheese, chicken, hot dog sausages chopped up, sprats... Squeezy cheese is also a good one although not easy to throw! He may not be eating well because he's lonely, sad, anxious, as well as not getting his usual exercise and mental stimulation.

My only other suggestion is to see if someone the dog is already comfortable with / used to could help eg ex partner, old friend who's been to the house lots.