Rule of Thumb for gold proof premiums

[SouthCoastInvestor]

Does anyone have a "rule of thumb" for premiums on (modern / non-rare) gold proof coins on the secondary market (assuming the coin is in mint condition - i.e. unhandled)?

I find it difficult to know what represents good value with these kinds of coins.

It is not always possible to find current data on actual sale prices, and if I am out and about I may not be able to get an internet connection.

For example, there is a gold jewellery shop / scrap dealer near to me who often has interesting pieces in his window, such as Britannia proof sets from the 1980s, 1990s.  I bought from him a 1/10oz Belgian proof Euro coin at 40% over spot, I loved the coin, but not sure if that was a deal or not.  On other occasions I have bought proof coins at close to bullion premiums at coin fairs, I suppose these are ones that are just not particularly desirable designs.

It would be useful to have a "rule of thumb" for purchasing.

What is a crazy premium for a pre-owned proof coin?  50%?

I am not talking about ancient or rare coins.

Thx.

 

[MoralHazard]

I think anything over 10% is crazy. Usually can buy for same or less premium as normal bullion that is 3-5%. Sometimes can find deals for like 1-2% less than spot

Proof coins are waste of money in my opinion. I can understand somebody buys one in silver here and there but in gold - the  base metal price makes these coins extrimely expensive and as I said waste of money

[DaKine]

That is rule of thumb for run of the mill. Some, like the 2014 Britannia simply will NOT be available at anything near that price. Please let me know if you can get issues such as the 2018 Proof Oriental Border Gold Britannia near those prices. 

I think your question posed is difficult to answer.