The compost I've bought in store in recent years has been very bad.. I buy peat free but the seedlings have not flourished and in some cases actually died. I found they fare better on my own home made seed compost but its the weeds that are annoying.. hence my sterilisation plans. The best compost I've come across commercially sold is Levington M2 ... at £8.50 for 75 litres its not cheap but it looks as though it is not like the chain store stuff which seems to have bits of all sorts of waste in it... plastic, lumps of wood even bits of alloy foil and pieces of metal I've served out. I don't buy seed compost as it is a frightening price !
I'm hoping my plan for home made seed compost will work.