Learn Finnish: Tarjous on varmaan liian tiukka. - The offer is probably too tight.

In everyday Finnish, varmaan is mostly used to mean 'probably' or 'I guess'. If you want to express that something is absolutely certain without a doubt, it is safer to use the related word varmasti (certainly/definitely).

What kind of 'offer' does tarjous refer to here?

Tarjous can mean a formal business offer, quotation, or bid, like in this sentence. However, it is also the standard word for a 'sale' or 'special discount' in a shop. You will often see store signs saying tarjouksessa (on sale).

Does tiukka only refer to physical tightness, like tight clothes?

It does mean physically tight, but it is heavily used metaphorically just like in English. A tiukka tarjous means an offer that leaves very little room for negotiation, profit, or flexibility. You will also often hear phrases like tiukka aikataulu (a tight schedule).

Since this lesson is about vaikka (although), how would I attach a vaikka clause to this sentence?

You would just add a comma and start the next clause with vaikka. For example: Tarjous on varmaan liian tiukka, vaikka yritimme parhaamme (The offer is probably too tight, even though we tried our best). The word order inside the vaikka clause follows standard main clause rules, making it very easy to use.