Hi DB, I’ll help as much as I can with this issue.
Just to make sure all our Ts are crossed and Is dotted:
You are anchoring your model on a well lit, horizontal surface with enough room that the camera can get a stable view, correct? I have to clear my desktop off to get a good read there and have better luck with the floor as long as there isn’t a carpet with a really crazy pattern on it.
The initial scale for AR will fit to the size of the plane you’re putting it in, so however much of the triangle mesh you see is the max size the model will start in. You can go in and change the scale from there, either manually by tapping and moving your finger on the screen or with the presets (1:1 for life size based on the size it’s modeled in SketchUp). You can also anchor your model in one spot and reanchor it somewhere else if you’re trying to move it a long distance. So you can place the model in a good spot for AR and then pick it up with Anchor and the model should move with you wherever you move.
Once the model is placed you can open the movement tab by tapping on the four directional arrow at the bottom of the toolbar. The Move tool lets you move the model with two fingers on the screen, the Rotate tool lets you rotate with a single finger and the Scale lets you scale the model up and down with two fingers in a pinch gesture. Just make sure you have the tool selected that you want to use (you can’t scale while you’re in the Move tool, or rotate while in Scale for example).
If none of this is helpful I might need more details from you on what specifically is going wrong.