You have the right to uninterrupted use, and they only have the right to access whilst you live there for a reasonable inspection and for emergency purposes. By law.
Bear that in mind.
Years ago we had the same, we were renting and our landlord decided to sell up. After having his whole estate valued he picked ours, it was we were told the easiest to sell because of how it was kept.
The letting place owner told us the bit I put at the top, and he said they (selling agency, his only did lets) will try to tell you are bringing people round all the time, be firm, give them windows of acceptable time, so say these 2 nights a week between 6-8 we are happy for you to show people round as an example, which I did, iirc tuesday and thursday.
I still remember it now, a phone call around lunchtime, oh hi, we are bringing someone round this afternoon, will you be in or out, no worries we have been given a key.
I said well you better cancel, I already told you when you can come, and if you do so outside that time I will call the police. They went quiet and eventually said ok.
They didn't turn up, I went home to make sure.
They arrived on the first window I had given them, was next day iirc, and the house sold almost immediately. So we were fine, iirc we had two viewings and one of them bought it.
Our ex landlord was really happy with us, he actually sent us a case of wine for how we left the property.
TLDR the agency will likely be pushy, be firm and reasonable on when you accept viewings, they need to suit you, not them.
