I did not found issues regarding them here on this forum.
A lack of issues is not good enough.
If you do a web search for SafepayBTC you will find a handful of scam accusations, and zero good reviews. Just because there haven't been
a lot of scam accusations doesn't mean you should trust them. You should be looking for an escrow who has an extensively documented trading history and a number of positive reviews. Their website doesn't even use HTTPS. Big red flag. I'd also be very wary of the seller who is recommending the shady service to you. Are they reputable? Do
they have a positive trading history? This could well be a scam.
Just because the seller is a third party doesn't mean you can't use one of the suggested forum escrows. In fact, the seller refusing to consider an escrow which you have suggested makes me think even more that they are trying to scam you.