Here are the completed sentences with explanations of the verb forms used:

1. **(be)** There **had been** ten years before.
- **Explanation:** Past perfect is used to indicate a time before another time in the past.

2. He **gave** me advice after I **made** the decision.
- **Explanation:** Both verbs are in the past simple; they describe completed actions in the past.

3. On my last visit to my hometown, I **found** that it **had not changed** much.
- **Explanation:** "Found" is in the past simple, while "had not changed" is in the past perfect, indicating the status at the time of the visit.

4. My boss **came** into the office just as I **was showing** everyone my holiday photos.
- **Explanation:** "Came" is in the past simple and "was showing" is in the past continuous, showing an action that was in progress when another action occurred.

5. A friendly American couple **started** chatting to me as I **was checking** in at the hotel.
- **Explanation:** "Started" is in the past simple, while "was checking" is in the past continuous, indicating an ongoing action interrupted by another action.

6. The soup **tasted** much better after she **added** more salt to it.
- **Explanation:** Both verbs are in the past simple, describing two completed actions.

7. They **had come** round to look at the house three times before they **decided** to buy it.
- **Explanation:** "Had come" is in the past perfect (indicating actions completed before another past action), and "decided" is in the past simple.

8. I **hoped** to go away this weekend, but my boss **gave** me some work that I had to finish by Monday.
- **Explanation:** "Hoped" and "gave" are in the past simple, while "had to" indicates an obligation in the past.

Feel free to ask if you have any further questions!